Watts Instant Hot Water Recirculating System

If you’re tired of watching water go down the drain while waiting for it to heat up, the Watts Instant Hot Water Recirculating System may be just what you need. The pump attaches to the hot water line at the water heater to circulate hot water throughout the home. A programmable timer can be set to turn the pump on only during the hours when hot water is typically used. The kit comes with everything you need and can be installed in under two hours. The Watts Recirculating Pump is available from The Home Depot for around $200.00.


  1. Re.: Watts Instant Hot Water Recirculating System.
    To: Danny Lipford
    1)If recirculated hot water is now in the cold water line isn’t water wasted while waiting for cold water to appear at the cold water tap?
    2)Does the cost of electricity to run the pump and the extra cost of fuel to maintain hot water temperature in the hot water heater negate the savings realized? Add to that the loss from 1) above.
    I am interested in your opinion and what Watts has to say.
    Thank you, Ronald B.

  2. In addition to questions raised by Ronald B., Nov. 28, 08, 8:16pm, does the hot water have to run constantly? If I set my timer to come on at 8:00 am, go off at 9:00am, then come on again at 8:00pm, shouldn’t the pump stop working during the down time. When I feel the hot waterline during down time – it’s always hot/warm. Is this normal? As per Ron B., does it increase electric bill and gas bill? So far the pump does what they say – – it puts hot water to the “back forty”.

    William Ray

  3. I had a recirculation pump with a dedicated return line and a timer but it had two problems:

    1) Most of the time the pump is running, it is not needed
    2) when Hot water is needed, the pump is often not running.

    I solved the problem with a unique “on-demand” control that turns on the pump when the hot water anywhere in the house is turned on.

    A diagram of the solution is at:

    1) On the cold water IN on the Hot Water tank, a flow switch is installed that turns on when it detects flow. (Note: This can *not* be anywhere in the circulation loop)

    2) A Delay-Off timer turns the pump on immediately when the Flow Switch turns on, but does not turn off the pump for a while after the flow switch is turned off. (The delay time needs to be adjusted for the characteristics of the particular installation. Typical times range from 30-90 seconds)

    3) An aquastat is used to turn off the pump when the farthest faucet in the loop reaches temp.

    When the hot water is turned on, the pump comes on and hot water arrives very quickly (but not instantly). The innovation is this: Turn the hot water on for a second and then turn it back off…and the pump keeps going for a while. Then just wait for a little bit and turn the Hot water back on…it is hot and ready to use. After the water is turned off, the pump will run for the delay time and then stops till the next time there is demand.

    The parts I used for the controller are:

    Flow Switch: Gems 26605 (I got it cheap on ebay). (http://www.gemssensors.com/ApplicationSearchResults.asp?nQuestionID=36 ) Others are available, but be sure to get one that has a fairly low trip point on the flow. (.75 – 1 GPM)

    Delay off Timer: MX046 timer kit. (15 second to 6 min delay)
    (http://www.bakatronics.com/shop/item.aspx?itemid=466) It is inexpensive but you must build it into a case. There are other delay-off timers and relays available but this seems to be the cheapest option.

    Aquastat: Grundfos ½” Clip on.

  4. I can easily see where this device is a huge energy waster. First off, it appears to run constantly when you tell it you want hot water. Electricity is wasted there. Secondly as soon as you remove the hot water from the tank it starts to cool off. The further from the W/H the water gets the more heat it looses. By the time the water gets back to the tank it will need to be heated again causing the W/H to run almost constantly the entire time this recirculator is on.

    The purpose behind tankless water heaters is to save energy by not needing to constantly reheat stored water. You turn the spigot on and the tankless heats the water at the instant it is needed there-by saving energy.

    This recirculator does the exact opposite by taking heated stored water and running it out through the house and loosing heat.

    This device gets a big, big, big, thumbs down from me.

  5. Richard,
    Recirculation systems have their place and tankless systems have theirs. It’s all choices and trade offs. Each person makes decisions based on their particular situation and what they find important (or not).

    If I were building this house new, I *might* consider putting in the Electric or Gas lines, the extra space at the faucets, and the 4 tankless systems the house would require but does not have now. As it stands, the system in my house had a recirculation system on it. I had to make trade-offs around ease of installation, Cost of istalation, operational costs, convienence, energy loss and water loss… and I found a way to significantly improve it. I am satisfied with the result and I suspect that others might find the idea usefull. However, as you point out, others (with different value sets) won’t find the ideas usefull. Ain’t the web wonderful!!! 🙂

    BTW… Take a look at the diagram at:

    I have an aquastat on the system… the pump does not run the whole time hot water is being used. It only runs till the HW feed is hot. And yes, this cools back off afterward…but it beats running the pump 24/7 or on a timer.

    BTW2: For those that *do* find the idea interesting: I had a typo in my parts list. I used a GEMS 26615 Flow Switch (Not 26605 as stated above)


  6. Paul,

    I like your idea a lot! I have been looking for a convenient yet practical means of circulating hot water when needed without relying on an inflexable timer schedule or having to put switches at each location. What a great idea, using the tap valves as a switch! I can probably get rid of my 10 gallon electric heater that I’m using to keep the circulating water hot. I put it in the system so that the tankless heater would not have to run while the pump was on. With your system, and a little fiddling with the delay, I think the tankless unit can manage everything just fine. What type of heater are you using?

    Richard, I didn’t hear any suggestions on a better system from you. Care to add anything?


  7. 3 days ago I installed the Watts pump. There is warm water in the cold line to begin with but because my problem was running the hot water line until the flow heated up(sometimes that took 3 to 4 minutes) I don’t find that to be a problem. I get my cold water to drink from the fridge if I need it. It was easy to install and has worked out great for my household. We are going on water meters soon and the local utility recommends this as one approach to save water.

  8. I want to install the watts model recirculating system sold at Home Depot but I worry about the heat-up factor in the cold water line. How effective is the control valve at stopping the recirc flow against the operation of the pump once the hot water line has achieved temperature? Any thoughts on watts versus grundfos? Does one make a better isolating control valve than than the other?

  9. Paul – thanks a million for this info – sounds like a great solution.

    I have no water recirc system yet and was looking at a chillipepper 6000, a redy temp, or a pump type system. The on demand setup seems best and your solution is pretty neat.

    Would like to learn more and I will look into the Watts system mentioned here.

  10. Paul,

    Thanks so much for sharing your solution. You’re a godsend!

    I’m building a house, and after the plumber put in the pipes for the recirc, he casually tells me, “Just so you know, it’ll take maybe 4 minutes to get hot water to the kids’ bathroom when it’s outside the timer’s operating time, because that bathroom’s last on the loop, and the hot water now has to travel over the entire house.” I asked for solutions, and his only advice was to run the timer much more often or run down to the water heater to manually turn on the pump (he’s not even aware of remote switches!). I wanted to throttle the guy. Had I known that, I never would have opted for the recirc system in the first place. And as you know, when a recirc system runs too frequently, it costs a bundle in energy losses (heat leaking out via the hot water pipes).

    Your solution is ingenious. Thanks again.

  11. Paul,

    Quick question:
    If you have the aquastat, why do you need the delay-off timer? Couldn’t the flow-switch trigger the pump on and the aquastat turn it off (or prevent the pump from being turned on again), making the delay-off timer unnecessary?

    I’m totally new to all of this and am just trying to understand your solution better.

    Thanks again so much.


  12. Folks,
    I have been away from the forum for a while… Sorry.

    Jim Asked: What type of heater are you using?
    Answer: 40 Gal Natural Gas. I think it is from Home depot.

    Newbie asked: If you have the aquastat, why do you need the delay-off timer?
    Answer: The delay off timer allows you to momentarily turn the Hot water on to start the pump. You can then turn the water off but the pump keeps running to prime the system. Without the delay-off timer, you would have to leave the hot water running. This would still be faster than without the pump…but water is still going down the drain.

    While we are talking about the Aquastat: I am still not 100% satisfied with it….It takes too long to respond so the pump is running longer than it needs to. When the system was on a timer that ran hours at a time… this was fine. However, I am trying to think of a low cost Aquastat that would be more responsive… Ideas are welcome.

    BTW: I picked up a used run-time meter from a local junk electronics store ($5) and put it on the pump. It turns out that with a family of 4 (3 home most of the day) the pump averages a little under 2 Hrs/day. This is more than I expected but is still a lot less than the 5 hrs/day when I had it on a timer. Furthermore, the 2 hrs are guaranteed to be while the Hot Water is in use. I might be able to reduce the 2 Hrs some by fine tuning the Delay-off time..but I have not done that yet.

    Here are some pics:
    The Flow Switch:

    The controller:

    Inside the controller:

    Cheers and good luck.

  13. Greg,
    I think I mis-understood your comment. A gentelman on a different forum asked a similar question…and I think I finally understand. It is a great question and it may result in a significant simplification of the original idea.

    If I move the flow detect switch to the Hot Water *out* of the water heater, I might not need the delay-off timer.

    A diagram of the idea is at:

    The basic idea is that once the flow switch turns the pump on, the flow from the pump keeps it on….till the aquastat turns it off. Simple and Elegant… I love it!!

    Warning: I have not tried this idea yet…… But I probably will. 🙂

    If someone wants to try it, there are a few things to think about:
    1) The flow switch must ‘trip’ on the flow from the pump. This probably means you want to stay with a .5 GPM flow switch.

    2) The Aquastat needs to be able to react quickly to the temp change. Otherwise the pump will run for longer than is necisary. The clip-on Aquastat I currently have is *not* fast enough for this idea.

    3) To get the system going, you probably need to turn the Hot water on for a few seconds longer than with the delay off switch. (The pump has to get the water moving fast enough to keep the flow detect switch ‘on’ before you can turn off the water and still have the pump run.) This is another reason to stay with a .5 GPM flow switch.

    If you do try it, Please post your results.

    Good Luck

  14. Paul,

    One thing I like about your original design is the ability to manually turn on the pump with the switch you put on the timer. That is great for maintenance and purging the air from the system.

    Thanks for taking the time to document your success.


  15. Paul…

    One other question, couldn’t you adjust the response time on the aquastat by moving it closer or further away from the heat source. ie… If yours is triggering late, move it closer to the tank and it should trigger sooner???


  16. Chuck,
    I have thought about your idea of moving the aquastat closer to the heat source and will probably give it a try. Right now I am back-logged on other honey-do chores but hope to get to it soon. 🙂

    Also, having the switch at the timer IS handy for maintenence.


  17. I want to install a watts recirc system with a timer. Will I be able to get hot water if the timer is off?
    What about using the watts system with a dedicated return line and not using the cold line for return?



  18. I installed one of these about a month ago in our house with the parts included in the box. I have noticed quite a difference in how long it takes the water to heat up when the pump is working compared to when it is not! I have the timer set when my wife is getting ready in the morning and when I would normally be cleaning up from work in the evening. I have also used the hot water in the showers (both upstairs and downstairs) at other times and it has taken longer for the water to heat up. I would recommend this to those who ask about it!

  19. Paul,

    I set up the revised version of your idea today into my tankless water heating system. I see a slight reduction in the time it takes to get hot water but not much. I also can’t get the circulation flow alone to keep the water heater fired up if I turn off the facet. I have a Paloma tankless which is supposed to respond at .6 gpm. http://www.tanklesswaterheaters.com/ph28rdv.html

    I believe I am getting too much back pressure on the pump which why it is fairly ineffective if the facet is off. I must be getting at least .5 gpm because the flow valve is staying energized but I don’t seem to be getting the .6 gpm to keep the heater fired up. I am suspecting the water pressure from the city is too much for this little Watts pump.

    Any suggestions on how to increase the flow in the circulation loop. I may move the circulation loop so it is going strait through the T connector and have the city water coming in the bottom of the T. I don’t know how much difference that will make but I am out of idea’s.

    I may also try to find a Y connector to replace the T. Maybe that will give me that little more humph I need…

    Anyone have any suggestions?



  20. All,

    I called Paloma and it seems Watts and most circulating pumps are considered “low flow” pumps. You need a bigger pump for a tankless system with return loops. The low flow will work fine for comfort systems when you use the cold water for return but if you want a dedicated return you must use a larger pump. They said the only one that works reliably was the Grundfos UCT-909. They are made for tankless heaters.

    More money, more money…!


  21. Chuck…
    Sorry to hear it did not work well :-(. I am currious what model/brand pump you are using…? I am using a Grundfoss UP 15-18 SU. (I think it has been replaced by a different model). I have never timed the difference with and without the pump but it seems to move enough water to really make a difference. I guess I need to put a stopwatch on it….

    Meanwhile…. I ordered a White-Rogers 1127-2 strap-on aquastat (cheep on E-bay). I hooked it up next to the pump at the Water Heater….and it makes a big difference. It reacts very fast to the changing temp and shuts the pump down quickly. I have a run-timer on the pump and before the new Aquastat the pump was running just under 2 hrs/day. With the new aquastat it seems to be about 20min/day.

    Next-step: Reconfigure to the new design (Without the timer).

  22. I had found a cheap Watts pump http://www.wattspremier.com/watts/showdetl.cfm?&DID=15&Product_ID=181&CATID=1 off eBay. I moved the pump to the strait through portion of the T connector and it does work somewhat now. I only save about 5 seconds for initially getting how water but once the loop kicks in it brings the water up to temp in the pipes which really makes a difference. I don’t have to remember to turn on the shower before turning off the sink after shaving and brushing my teeth. The dishwasher and washing machine work better also.

    I see what you mean about the aquastat. That thing still runs a good 4 or 5 minutes after the sink has hot water. An aquastat comes with my new pump so I may extend it to the copper pipes since I have PEX by the pump.

    The difference in the Laing UCT-909 is it can take 24 ft of head and pumps up to 6 GPM. The Watts has 3.5 ft head and max at 3.4 GPM. The extra head will allow it to give a good flow while pushing against the city water. I am thinking of moving the check valve I have now to the supply from the city water since the pump comes with a built in valve.

    I appreciate your inspiration and documenting your success so thoroughly. I will sell the old Watts pump on eBay so it won’t be a total loss…


  23. Chuck,
    You mentioned: I am thinking of moving the check valve I have now to the supply from the city water since the pump comes with a built in valve.

    Carefull…. I have heard that in some areas, building code would also require you to add an expansion tank somplace on the hot water side. The concern is that as the water heats up and expands it needs a place to expand too…If you have a check valve, the expansion preasure can not back up into the city pipes.

    There may be something too this. While I installed my flow switch and timer, I turned off my HW heater. When I turned it back on, I happen to notice that the cold-in pipes got hot a good way back from the HW heater. At first I was concerned I had some kind of back-flow. However, I have never noticed it again (And I checked it a lot). I think what happened was that as the cold tank heated up and the water expanded, it backed up the pipes…the only place it could go.

    Also, years ago my boss had a check valve on the cold-in and got a bad knock every time he turned off the Hot Water. He never could explain what was happening, but when he took it out, the knock went away. (He was the guy that first told me about circulation pumps)

    Good luck

  24. Thanks for the advice, I guess I won’t put that valve there cuz you makin some good sense. All the pipes I put in were PEX which I understand expands but no need in taking unnecessary risk…



  25. I’m getting ready to install a recirculator and am fascinated by this modification. My 1st question is: how do you know which faucet is the last one on the circuit? I suspect it isn’t always the one furthest from the water heater. I have a small 3br/2bath ranch and it seems the kitchen sink is slowest to receive hot water, yet other than the washing machine, it’s closest…as the crow flies.

  26. Laura
    You asked: How do you know which faucet is the last one on the circuit?

    This is hard to say. Typically the farthest from the HW heater would be the ‘last one’. However, not all houses are plumed on a ‘circuit’ some will fan out from the Hot Water heater on different lines. (This makes a circulator very difficult). You can bet your house was laid out in whatever way was easiest for the plumber.

    Is your ranch on a slab? A Basement? A Crawl Space? The best way to tell the layout is to look at the plumbing (if you can see it).

    From your description I am guessing your HW heater is in the garage, next to the kitchen. Typical for a 3BR/2BTH ranch would be the two bathrooms are next to each other at the opposite end of the house…or one in the middle and one on the far end of the house…???? If this is the layout The farthest bathroom would almost always be ‘last’. However, it is strange that the kitchen is slowest to heat up. I would *guess* there is something funny on the faucet at the kitchen sink and you are not getting much Hot Water flow.

    Is there already a return line for a circulation loop? (This is not typical) The reason I ask is that my house is also a 3/2 ranch and does have a dedicated return line. Unfortunately, at some point during a remodel someone put the kitchen sink on the return loop… That means the hot water goes all the way to the far end of the house and back to get to the kitchen. :-(. Someday I am going to fix that but I would have to do some digging in the crawl space to get to it…. not a fun task.


  27. Chuck:
    You said:
    “The extra head will allow it to give a good
    flow while pushing against the city water.”

    Actually, in a closed loop circulation system, the city preasure does not make a difference. (The ‘Head’ on a pump spec is measuring the difference in preasure on either side of the pump and when the pump is off, the city preasure will be identical on both sides of the pump.) However, the greater ‘head preasure’ of the pump will allow the pump to better overcome the fluid resistance of all of the pipe in the loop.

    BTW: I was just out on EBAY and saw several Grunfos pumps that looked like they were going to go fairly cheep. I don’t know what is needed for a tankless, but the UP 15-42 SF looks like it would make a nice circulator and there are 3 that are probably going to go for ~$50.

    You can get specs on them at:


    Note: I have the UP 15-18 SU (Grunfos has replaced that model with the UP 15-29 SU)


  28. Well, my Laing UCT-909 arrived and what a POS this pump is. There is no mechanical connection between the motor and the pumping rotor. I hooked it to the water hose and saw no difference between it running or off. Can you actually see the Grunfos pumping? I am really disappointed with this Laing UCT-909… The Watts barely works with my system but it works a whole lot better than this Laing UCT-909. And was a lot cheaper…


  29. Paul,

    Here is what I believe is happening with the new design and my tankless heater.

    The pump turns on fine when the water is turned on.

    However, when you turn the water off the change in pressure seems to open the flow switch just long enough to turn off the pump. I find if I keep quickly turning the water on and off enough times I can get it to take and the pump will continue to run. I can see the heater turn off but onces things stabilize in the pipes the heater comes back on.

    The delay timer in your original design seems to work better for a tankless system. It keeps the pump running when the facet is closed so that onces things settles down in the pipes the tankless heater will feel the flow from the pump and come back on and begins heating the loop with no water being wasted. This doesn’t happen if the flow switch opens when you turn off the facet since it will turn off the pump and ruin the whole effect.

    i am not sure if that makes sense but that is the best my non-technical mind can fathom.

    Now maybe you can help me again… My house has basically two branches. One branch off the mainline that runs to the downstairs bathroom then feed up the wall to the upstairs bathroom. The mainline continues past that branch off and terminates at the kitchen sink.

    I spent a lot of time putting my dedicated return loop close to the kitchen sink thinking it was the end of the line. I made the mainline and return loop 3/4 but the branches to the bathrooms and kitchen are 1/2. My logic was if the mainline and loop were 3/4 they would be less resistance and carry the bulk of the water while the pump was on.

    I see a difference in the bathrooms (not much but some) however it actually takes longer to get hot water in the kitchen. I suspect the open kitchen facet poses less resistance to the water than the return loop so the majority water is coming out the facet instead of circulating around again.

    I am scratching my head trying to figure out the most efficient design for my house. How did you create your diagrams? I would like to diagram my house and put it up for all to see so that someone may suggest a better way to hook this up.

    One thing I have determined, I think the less 3/4 and the more 1/2 pipe you use is better since there is less water to clear before getting the hot. I know this because I have been doing just the opposite and removing 1/2 and adding more 3/4 thinking it will be less resistance and each time I add more 3/4 I increase the time it takes to get hot water.



  30. Chuck,
    Let me answer the easy one first:
    >How did you create your diagrams?.

    I used powerpoint to draw them up. I then selected everything in the diagram and did a right-click. One of the options in the right-click menu is “save as picture”.
    (I am using Office 2007… I do not know if this works in earlier versions)

    > when you turn the water off the change in pressure seems to open the flow switch just long enough to turn off the pump.

    Interesting… I would not have expected that. I have not tried the 2nd design yet….but you really have my curiosity going. It is almost like a shock wave (like what causes pipe Knock) is throwing the switch. However, even then, I would think the momentum of the water in the loop would keep the switch on and the pump going.

    > it actually takes longer to get hot water in the kitchen.
    This is sure counter intuitive….

    I will have to think about all this for a bit.

    Some questions for you:
    * Is your pump on the return loop or on the HW main? (It is typical to put it on the return loop)

    * Is there a check-valve in the return loop? (and is it installed in the correct direction?

    * Are you using the UTC 909 pump mentioned before? (I want to look up the specs of the pump you are using.

    * Is the run from the Downstairs bath to the upstairs bath very long?.

    As far as 3/4 vs 1/2…. You are correct, 1/2 is going to tend to hold less water and therefore the pump will flush it out quicker. On my system the main is 3/4 and the return is all 1/2. My gut tells me that you should either make it all the same size, or put the larger pipe on the main and reduce it down for the branches and return. Having larger pipe on the return seems wrong to me….but I could not tell you why it wouldn’t work.

    Note: On some forums, people have mentioned that for continuous running Hot water loops, you can actually ware out the pipes due to chemical reactions that are accelrated by the moving water. The claim is that using larger pipes will slow down the water and reduce the ware.
    Since we are minimizing the time the pump runs with our designs I don’t think it really applies to what we are doing… but I thought I would mention it. (I will try to find a link and post it)

  31. Guys…

    Here is an idea of how mines looks. I changed the dotted line today to make the loop go strait through the T which brought the kitchen down to 45 seconds from just over a minute. I also installed the delay timer from your setup which overcomes the flow switch problem because the pump keep pump through the pressure surge.

    Now my problem is the pump isn’t sucking enough to keep the tankless heater fired up. Because of the delay timer the pump is running fine but the flame on the heater goes out.

    http://www.tanklesswaterheaters.com/ph28rdv.html Here is my tankless heater. The problem is I need .6 gpm of suction on the output side to activate the burners but the pump is pointing into the input side. I don’t think it matters how much pressure I put on the input side, the city water doesn’t activate the heater so I don’t think any pump will.

    http://www.lainginc.com/pdf/UCT-909%20Tankless%20Brochure.pdf Here is my Laing pump I think it does pretty good on the output side but it doesn’t have much suction. I don’t think it sucks enough from where it is in the loop to put the .6 gpm demand on the input of the heater. I know this because I stuck the pump inlet in a bucket of water and it doesn’t create a lot of suction. It does better pumping with the pressure from the water hose.

    http://www.wattspremier.com/watts/showdetl.cfm?&DID=15&Product_ID=181&CATID=1 The old Watts pump sucks a lot better. I get a good stream shooting in the air from it when I put it in the bucket but I don’t think it’s enough flow to keep the flow switch activated so when the timer runs out the circulation loop stops. I could bump up the timer but I want it to work as designed 🙂

    I am thinking of leaving the Laing pump where it is then putting the watts pump close to the output from the heater. My logic is the watts will give me the .6 gpm of suction I need to activate the heater and the Laing will give me the circulation in the loop to keep the flow switch activated. The watts has no flow valve so it is a strait through shot when it is off and no noticeable resistance. I think I put both pumps on the AC out from the delay timer so they will turn on and off together.




  32. I think I sorted out the problems with my system…

    The pump is actually working when it turns on, the problem is it is seldom turning on. I have the water heater set at 125 degrees. The aquastat that controls the pump opens at 105 then closes again at 85. It doesn’t take long with that 125 degree water to turn the aquastat off and the pipes don’t loose heat fast enough to get the water under 85 degrees so the only time the loop works is after the water has sat more than 2 hours.

    I guess what I need is an aquastat that works at a much higher temp. Maybe open at 120 or 125 then close again at 110 or 115. Any suggestions would be greatly appreciated.


  33. I reciently installed a tankless hot water heater and now realise I need a recirculation pump for obvious reasons. I got the Laing UCT 909. It seemed to be the one I would need according to the specs. The unit I replaced was a 40 gallon tank water heater with a 1/2″ return lineto a recirculation pump. The gunk that accumulated in the brass portion broke the stems of t valves. Being my floor is a cement slab, I cant figure if the line is dedicated. It seems to be the way it was plumbed. What I need now is a schamatic that would identify the position of all the components in installing the recirculation pump / check valvue, etc.
    Thank you in advance.


  34. Dan
    I just bought a house with a hot water recirculating pump. (It is tied into the cold water side)It seems to work fine for the first four, five minutes then the temperature gets hot than cold than hot than cold. What could the problem be its driving me crazy. I have had a new hot water tank installed and a new recirulator pump installed with no help what so ever.Any suggestions would be appreciated.I am thinking the plumbing is wrong…

  35. Vic,
    The two critical components are the pump and the check valve. (I looked up the UCT 909 and the check valve is built into the pump so you do not need a seperate one)

    Typically, the pump and the check valve are on the Hot Water return line (I don’t think it matters what order) and feed into the Cold in to the water heater (It has a ‘T’ with the cold supply). On traditional HW tanks, some people will feed it into the outlet for the drain valve at the bottom of the tank….but that is probably not an option on a tankless.

    Once the pump is installed, you have to decide how to control it. The UTC 909 also has a 24 Hr timer and 130 degree Aquastat built in… so you are all set for the the typical controlls on a circulation pump. All you have to do is set the timer for when you typically use Hot Water.
    (This is the way the vast majority of closed loop recirculation systems are controlled)

    Some of us on this thread want to try to do something better than the timer (primarily for 2 reasons).
    1) sometimes you want hot water when the timer is off.
    You still get HOT water…but if the pump is not
    running you have to wait.

    2) A lot of times the pump is running (waisting energy)
    when you are NOT using the hot water.

    If you are interested in tinkering with the way the pump is controlled… I encourage you to read the posts above from myself and others.

    Good luck

  36. Dan,
    Have you figured out the problem?

    Can you tell us more about the installation. Is this one of the open-loop under-the-sink circulation systems or is it a closed-loop system with the pump at the hot water heater?

    If it is a closed loop system, I am not sure what could be causing what you describe. However, you may want to check to make sure there is a check-valve someplace in the loop. I would also wonder if something is wrong with a single-handle valve someplace in the system (letting cold water somehow get in) However, I am not sure how either of these would make it alternate from hot to cold.

    If it is an under-the-sinc open loop system, I would suspect something on the by-pass valves that hook into the cold water side….
    NOTE: I am not experienced with open loop (under sink) systems, so I am just guessing based on what I have read about them.

  37. Dan,
    Assuming you have a closed loop system, an Aquastat, and either no check-valve or a stuck check-valve, here is what *might* be happening.

    1) Pump comes on
    2) After a while, the aquastate sensis the system is ‘at temp’ and shuts off the pump.
    3) With the pump off, the lack of the check-valve allows the cold water to back-up through the return line.
    4) This cools off the Aquastat and turns on the pump…making the water hot again…
    5) The Aquastat heats up, turns off the pump… and the cycle starts again.

    Without knowing your specific set-up, it is hard to say this is what is happening…but at least it is a feasable explination. If you can check if the pump is on when you get the hot and off when you get cold…it would help confirm the idea.

    Note: I do not know as much about the under-sinc, open-loop systems, but I could imagine similar problem might be happening with it as well.


  38. Chuck,
    I recently had a house built and have 2 – 7.5 gal Noritz tankless heaters installed in a series. The house is energy efficient, so I did not want a recirculation pump. Now that I am in the house I realize how bad I need one. It takes 2 minutes to get hot water to the shower, and even longer to the faucets. I wanted to know if Chucks design is common knowledge to a plumber or should I tell them thats what I want? I can not do it myself or I void the warranty.

    Which of the designs is the most energy efficient? They all seem to have good response times and reduced the time that the pump is actually on.

    Any insight would be helpful.

  39. Paul,

    My loop is working much better with my new aquastat. However, I believe the system can be further improved. I believe the limitation with my recirculation loop is that the water has no where to go. Yes it circles water back around and through the heater but it competes with the city water on the input side of the heater. My calculations, my loop is flowing at .5 gpm… The pump is rated at 6 so I know I can do better.

    What I think I need is some kind of tank about 2.5 gallons in size which will quickly accept the water from the loop when I first turn on the water then slowly release it to the input side of the water heater as the water is being used. I was hoping the expansion tank would do this but either I don’t have the air pressure just right or I am not getting an increase in pressure when the pump turns on.

    Any thoughts on a tank or bladder like this? Something that can quickly take about two gallons out of the loop (say 20 seconds or so) then slowly release it back into the cold side of the heater while we shower or something?


    It is not my design. I don’t want to take credit for others work. I doubt if your plumber will have this type design in mind but I think if you show them Paul’s drawing a few days in advanced they can certainly put something together. I would suggest getting the flow switch off eBay in advanced since they are very expensive to buy retail. Like $200 expensive. I got mine off ebay for $40 plus shipping.

    You might also let them install the recirculation loop then add the flow switch and aquastat yourself later on.

    Good luck and let us know if you need more input, I am glad to tell you what I have learned so far…


  40. Dan Risley…

    Is that a tankless system you have? The reason I ask, one thing I’ve learned is when the input water gets close to the temp setting the burners will turn off because there is little difference between the input and output temps. If cold water then comes you will get approximately 6 seconds of cooler water before the burners come back up to temp.

    I don’t know if this is your problem but it is something I have seen when my water temp was set lower than my aquastat.


  41. Paul,
    I am meeting with my plumber tomorrow and will show them your design(s), get your copyright material together..lol

    Thanks for the feedback Chuck…

    I will let you know how it goes.

  42. I only have a master bath and laundary that are at the end of my hot water line. I have a dedicated recirculation line and I installed my pump (grundfos up 15-29su) at the end of the line near the washer( You don’t need to put the pump near the water heater). I wired the pump into a 15 min timer switch like you see in public restrooms. That switch is in my bathroom which is just on the other side of the wall from the washer and the pump.I just set the switch at 5 min before washing cloths or taking a shower. I don’t waste elect, water, or gas.Also insulate your hot water plumbing including the recirt line.

  43. Sorry folks, I have been away from the forum for a while..

    How did your meeting with the plumber go? I am currious.
    (My guess is he was more willing to try the second design (without the timer)).

    Did you ever figure out the low flow problem? The .5 Gal seems pretty low. I would *guess* it is back-preasure from the plumbing and a ‘temporary capture tank’ would not make much difference. What pump do you have? For most of the common pumps you can look up the Preasure/vs GPM chart. (A lot of them drop off very quickly with just a little back preasure) (BTW: Since it is a closed system, the preasure from the city does not matter… only the preasure *difference* between the input and output of the pump matters).

  44. Paul,
    Any thoughts on how your recirculation project will work on new construction using PEX pipe and manifolds to distribute hot and cold water.


  45. I would not buy ANY Watts Water product! I bought a “floodsafe” washing machine hose. Within a few months it put out a fine spray that seeped into the drywall and subfloor causing over $6000 worth of damage. Their insurance adjuster agreed that the damage appeared to be caused by the hose but then took the hose for an “independent evaluation”. Turned out Watts evaluated its own hose, declared “no manufacturing defect”, and refused to return the hose. So I had no proof. If you buy any Watts Water product, BEWARE. When I went on Amazon.com to look at other customers experiences with Watts, I found that they had an abysmal rating–numerous One-Star ratings! And don’t count on Home Depot to go to bat for you! They certainly didn’t for me.

  46. Hi,
    I have wirsbo pipes connected to copper fittings and was wondering if these recirculation pumps would cause them to leak at the connection points or burst.

  47. I bought a house with an electric hot water heater and circulation pump that was on a timer. Needless to say, my electric bills were outrageous. So, an electrician friend talked me into putting in a Rinnai propane Tankless System, run in conjunction with the circulation pump. You can see the configuration at http://www.childcaresystems.net/ Then click on Data Bug and then AUP. You should be able to see two pics of what was installed. The timer is still utilized and this configuration is still costing me too much in utility costs. I feel that I need to change the system similar to what Paul Rygaad posted in his blog on Dec 22, 2008. My electrician friend suggested that “you need a ball valve between the circulation pump and down to where it goes into the wall at the drain pan. So you can close the loop off. Then unplug the pump.” Can anyone advise me the best way to change up this system in order to get hot water on demain wihout having the circulation pump running for hours on end?

  48. SD Jim,
    I have had a tankless WH for 5 years and works great except I have needed a recircu;ator the whole time but haven’t got around to it. I have a dedicated recirc loop in my system and have installed the timer at the far bath as you did but have been trying to figure out best size pump. Is the grundfos 15-29 for a tankless ie is it strong enough to turn the WH on.

  49. Hello,
    Recently I purchased Watts Instant hot water recalculating pump model 500800 for my house. I installed unit according to directions, it works fine for faucets farthest away from hot water heater. However 2 faucets (master shower and kitchen) closest to hot water, I don’t get any cold water. Really hot water comes through cold pipes. I let it ran for quite some time still no difference water is sooo hot from cold pipes. Any solutions, I am ready to return unit back store.
    I called Watts support line, week later I got response that, my two faucets (one brand new) may be at fault ( I don’t by that).
    Any suggestion appreciated

  50. Response to Paul:
    Can you send me a photo of your water heater installation? And another one of the under sink? I don’t think that is an issue, but just checking. Do you get cold water at the location where the sensor valve is located?
    If you get cold water there, I want to check the photos. If there is an issue where the sensor valve is located then I suspect that the sensor valve isn’t shutting down the water flow once it gets hot. What should happen is that the sensor valve should shut completely once the temp at the valve is greater than 110 degrees. After that the flow becomes just a small trickle to keep the temp at the valve to about 110 degrees.
    email to me is jerryzimmer at comcast dot com
    Thanks, Jerry

  51. I just had a Watts water circulator installed by a plumber today. Unfortunately, a few hours after it was installed we noticed that we no longer have any hot water in the house! Burners are functioning in both water heaters. Is this because the hot water that previously sat in water heaters undisturbed is now being mixed with cold water returned via the circulator or could there have been a mix up in the installation causing this?

  52. Paul,
    I have a typical hot water system with a 40 gallon tank in my basement. I am very intrigued with your recirc solutions especially the idea of moving the flow detect switch to the Hot Water *out* of the water heater deleting the necessity of the delay-off timer.

    I am wondering if you or anyone has tried this idea on a tanked system yet and, if so, did it work?
    Thanks, Tim

  53. I had an idea using some inexpensive motion detectors instead of the flow switch. Please take a look at http://recircsystem.shutterfly.com/. The switches can be mounted in any room and have a selectable timer – 5 sec to 20 min. They also can handle 1/8 hp motors.
    With this strategy, the pump only comes on if the water temp after the last fixture is cool and there is motion. After hot water is delivered, the aquastat shuts off the system. My question is, is the UP15-29SU an overkill for a 3/4″ copper delivery pipe with a 1/2″ return? Any comments are welcome.


  54. I love the WATTS Hot Water Recirculating Pump with Timer. I don’t have to wait forever now to get warm water. Have it within 2 seconds now. Before I had to just let the faucet run for 90 to 120 seconds before water was warm. How much extra natural gas will it take over the course of a year because of this pump ? I don’t care. I want what I want and now I have it.

  55. One factor not mentioned yet is for those of us who have a solar water heating system, the additional cost of heating all the stagnant cold water is zero. My main problem with the recirculator is the cold water becoming hot (in the absence of a dedicated recirculation line).

    I’ve been using 2 Chilipepper pumps (one on each end of a long center-fed manifold) for just under 5 years and was pleased with the result but for 3 things:

    1) Cold water becomes hot (not Chilipepper’s fault)
    2) They are VERY noisy. One is installed under-sink, and the other under-bathroom basin. The one at the sink isn’t bad, but the one in the master bath is a real waker-upper in the morning.
    3) The first one just failed. I’m going to replace it with a Watts pump and my own control circuit (yet to be designed).

    Long-term, I plan to add a dedicated recirculation line (house is plumber overhead) in the future, but am not sure yet how it will be controlled.

  56. I have been installing the Grundfos retrofit recirculation systems with the sensor (bypass) valve that allows the hot to flow back to the water heater through the cold water line. I have also been installing Navien tankless water heaters that are designed for homes with Recirculation systems. They have a two liter tank built in with an integrated recirculation pump that works very well. Unlike Rinnai and Noritz, you can use this tankless water heater with a recirculation system (because it is designed for it) without any reduction in the warranty (15 years). Rinnai and Noritz both reduce their warranty from 12 years to 3 if you use a recirculation system directly with the water heater. We have always had to isolate through a separate small electric water heater to maintain the recirc. line and not reduce the warranty for Rinnai and Noritz installations.

    My question to the group is whether anyone has used a different pump with the Grundfos sensor valve? I have a house that we installed a recirculation loop for the downstairs, but the upstairs has a long circuitous route that takes forever to get hot water to the master bathroom. I am considering putting the sensor valve at the master bathroom. With the Navien, there is a sensor on the incoming cold water that determines whether the pump runs (in addition to the timer).

    Just curious if anyone has actually done this? Did the cold water line overheat? The people at Navien tell me that there is no warranty reduction in doing so. They just don’t know if it will work.

  57. Jeff,

    You have to also consider how much water you are saving. Here, the cost of the sewer is twice the cost of water. Also, you are paying for hot water whether the water coming out of the tap is hot or cold. The water heater has to recover the extra water you are using waiting for hot water. If you have a family, in most areas the system will pay for itself. If you are a retired couple, you will probably break even between additional fuel cost vs. water and sewer savings.

  58. Selecting Domestic Hot Water Recirc Pump – Tankless – no dedicated return line


    I’ve been following this thread with interest… but I have a slightly different twist… wanted to see what people thought.

    I am looking for a little help selecting a pump to drive domestic hot water recirculation in my home (I am the home owner). I have a tankless hot water heater and no-dedicated return line. I don’t have power available under the furthest two sinks!

    As far as I can tell none of the systems on the market will help me… requiring either a dedicated return line or power under the furthest sinks.

    So I got to wondering…

    What if I use the “return” values from Amstrong’s new Astro Express System http://www.armstrongpumps.com/astroexpress/Valve.htm (looks much more well constructed than the grundfos comfort valves.) These valves create a return path for the water from the hot to the cold pipes at the furthest two sinks – but don’t require power.

    Then get a suitably sized pump to trigger the tankless water heater – which I would mount near the tankless heater in the mechanical room.

    So the question is what pump to buy…

    I see from the Laing ACT-909 model designed for tankless applications, without a dedicated return but mounted under the furthest sink has a head of just over 25ft and max flow of 8.5GPM.

    So what I think I need to try (yes I recognize this is an experiment and it may fail!) is a “simple” pump (no timer, no temp sensor, no check valve – all of which the Laing ACT-909 has) with the following specs:

    – 25ft of head
    – max flow of 8.5GPM
    – 3/4″ connections
    – Thermally protected (in case the pump ends up dead-heading against the closed Astro valve… I plan to only turn the pump on* for just long enough to get hot water to the faucets)

    Can some one give me a part number for a Laing, Armstrong or Grundfos pump which would meet these specifications?

    Also… should I mount the pump before the tankless (on the cold water inlet – i.e. the pump is pushing water into the tankless) or after the tankless on the hot side – i.e. the pump is pulling water into the tankless)…or doesn’t it matter?


    * I will be controlling the pump using a computer controlled timer I already have (actually an X10 control system

  59. Hi,

    I just installed the Watts Instant Hot water Recirculating system. I’ve turned on the pump and waited for 45 minutes but the hot water is still not hot enough to bathe in, its just luke warm. Why would this happen and how can I fix it?


  60. Newbie question: when using the chilipepper type system where the recirc is accomplished using the cold water lines – will that work under a faucet that is a single handle hot/cold type. How does the hot water recirc if the cold is on also – or is the obvious answer to ensure the handle is opened to the far left/hot? Even so, what happens when the handle is opened to a blended position. Thanks in advance.

  61. Barry,
    The parts list on my link above shows the Heath Zenith SL-6105-WH sold at Home Depot. Remember, the system described was theoretical. I never tested it. Currently, I’m running a recirc system without a pump (gravity) and am very happy with its performance.

  62. I have had the Grundfos Comfort System for about 4 years. Over the last few months the timer has been losing the correct time. I set it to current time and less then 24 hours later it is off by 12 hours. Have not had any power problems and it is on it’s own outlet.

    Suggestions, thanks.

  63. Just purchased a Rheem Hybrid Electric Water Heater HP -50 would like to install in series my current 80 gallon electric water heater . Plan to shut of the electricity to the 80 gallon water and make all my hot water in the Rheem in the heat pump model only , The heat pump will make 12.5 gallon an hour. I have 8 people in household That is why I need the volume of hot water. The heat pump will run 10 to 12 house a day. I would like to put a watts Instant hot water recirculator between as follows
    Hot water comes out of the Rheem Hybrid Electric Water Heater into the 80 gallon water heater’s water cold side and then come out of the hot side of the 80 gallon water heater to home water system. At the last hot water point I will have a tee and a return line back to the recirculation pump and check valve before it tees into the cold water line of the Rheem Hybrid Electric Water Heater.
    My question is can I use a Honeywell Aquastat Honeywell L8124 to turn the pump off & on when line come up to desired temperature or fall below a certain temperature.

  64. Also it seem the Watts Instant Hot water circulator and the Grundfos circulator are on and the same. How does it compare to the Taco D’MAND Hot Water Recirculating System

  65. 2 comments:

    1. Since I live in South Texas, the problem with warming lines only exists for about 4 months. Do you see any problem with leaving the pump unplugged for the other months?

    2. I went down to the home center to take a look at the hardware. Much to my surprise the product has been taken off the shelf for investigation of a product complaint. Do you have any knowledge of such a complaint? The store is following corporate direction.

  66. Hi all,

    I do like the solution that Paul has presented but I think getting the Watts Instant Hot Water Recirculating pump is still a good idea if you’re able to have a dedicated return line. I have an open basement right now and I’m thinking of installing the pump on the hot water line and send a 3/4″ pex to a new manifold at the other side of the house and then sending a dedicated return line back to my HWT. So that would mean all the hot water items at that end of the house can get hot water way sooner since it’s right there.

    Just thought I’d throw that out to people.

  67. We are looking at a Watts Recirculating System, we have found that between Lowes and Home DEpot they carry different ones, Lowes system is #500899
    Home Depot is 500800. Does anyone know the difference between these and which is the best one?

  68. What happens if you install this without the sensor? I have no idea on which fixture is the furthest in my loop. I put it on one, and it drastically slowed the flow on three others. I don’t want to just try it on all the fixtures on the one end of my house, so I thought I would just not install the sensor. What will/can this do?

  69. I installed the Watts recirculator on my system in hopes of saving money. WRONG! I set the unit to only be on when I get up in the morning to get ready for work and in the evening for washing dishes, cooking, etc., then off when I go to bed. My gas bill the month before the install was about $17.oo. The next month….$79.00. I gasped, then immediately unplugged the pump. I may tinker with the timer and try using it again in winter, but for now it is staying off.

  70. I have a Taco Cartridge circulating pump (Model 008-BF6)with what I assume is a aquastat wired into it. The aquastat is a honeywell. It has a dial on the front that is adjustable from 100 – 240. Is this temperature readings?I keep trying to adjust it, but only get luke warm water to the faucets. Can you help?

  71. My house has a gravity/thermal fed feedback system. Hw tank water gently rises from basement to first floor because heat rises. Cold water returns to modified connection by drain valve on heater. Actually have two tanks so those connections are connected to each other. 100 feet away in master bath hot water comes out of faucet in one second. No pumps. Once you have instant hot water in sink or shower you will never go back to running water until it finally gets hot. The system predates me at this house and the installer (I met at a home show) said when the time comes he can install a tankless and make it work. .? Both tanks are 23 years old so that day is coming.

  72. Hi

    I am looking to set-up the Demand Sensing Hot Water Re circulation Control system that your diagram above. I cannot find the Flow Switch: Gems 26605 on the Gems site or anywhere. Is that the correct part number? I have a 20 year old Grundfos UP 15018 SF that seems to be shutting down more frequently. It has a built in aquastat. Have you ever heard of these malfunctioning? I’m thinking about replacing it.

  73. Watts and Grundfos systems have thermostatic valves that close at 95 degrees. This prevents “hot” water from entering the ccold pipes. If the valve “closes” at 95 that means the valve also “opens” when below 95. Regardless of temperature, water exiting hot water pipes is resupplied at the water heater using even more gas. Wifey insisted warm water out cold faucets was not acceptable in recipes and other kitchen prep. I agreed after I was the one to thedinner salad and rinsing chilled produce with warm water. So much for having a cold salad. water comes from one place, water heater. cold water for warm water means my water heaters doing a lot more heating. I chose to be frustrated once, paying for a higher priced solution instead of daily stress of hearing with not having cold water. bills and a happier wife, you can’t put a price on that, I’d pay 3 times more for those results.

  74. I have the Model 500800 and am having the problem with the sensor valve letting hot water run in to my cold water line. I did the test and it continued to run in to the cold water side. I think the sensor is a piece of junk and it costs from $34 to $43 to replace it. I will just continue wasting water and not recommend the Watts unit to anyone I know.

  75. I just today installed a Watts system and see that it is made by Grundfos (guess that is why they look alike and work similarly(. Took me some time to wire in a line to the water heater cabinet and installing the under sink valve was a chore for a 72 year old with Arthritis and Gout. But I “got ‘er done”! Now, I am waiting to see how it does in the morning when it is time to shower. Used to take longer than a minute to get hot water there. Played with it a bit this noon in the always on mode and saw about 15 seconds which is an improvement.

    I am not excited about the timer but will go with it for now, using it selectively. However, I like the idea of a flow switch or Piezo switches and receivers to set it up as a demand type of operation. The Watts unit could be left in always on mode and the 115 volt supply line could be switched off and on by some sort of power controller I think. I am going to monitor the cold water side too to see if I have any issues. Ought not to be much hot water in cold side when the pump has been idle for some time.


  76. I had some time to play with the new Watts Recirculating Pump. Without the pump on line, it would take 3 minutes for hot water to reach the tap at my back most bathroom. When the water was cold again, I turned the pump back on and it again took 3 minutes which tells me how long the pump needs to be actuated before using Hot water. Once the water is Hot, I found that after turning the Pump off, the water cooled from 106.5 degrees (My Hot Water temp set point) down to 104 degrees in the first 5 minutes then down to 100.6 degrees after 10 minutes and later, to 99 degrees after 15 minutes. I checked again at 20 minutes and found 99 degrees so waited until 45 minutes and the temp came down to 91 degrees. The outside temperature was about 52 degrees.

    I decided to set my timer tabs to turn on for 15 minutes at 5:30 A.M. then off for 15 minutes, etc. until about 9:00 A.M. I took my shower at about 7:15 A.M. and water was HOT! Had to turn blend valve to nearly 3/4 of full range to keep temperature cooler and comfortable. Seems like the staggered timing works okay at my home. Set on at some start time then off for the next Tab and on again 15 minutes later repeating pattern until desired stop time is reached. Or, set every other Tab to On.

    I guess there is no way around overcoming the long run of pipe time delay when the water is cold. But, turning the Pump on 3 minutes early works well. Using every other Timer Tab reduces the Electricity and Gas use by half of setting all the Tabs On for the desired time period.

    I am however, still not excited about the Timer’s lack of flexibility and am looking at setting up some sort of simplified Demand system using an External box with a standard Timer on it in parallel with an externally triggered “Off Delay” timer which would give me the Standard Timer function as well as a remotely triggered Demand Switch to allow both Timer as well as Demand usage. I hope it works. I can live with the Watts/Grundfos under the sink valve.


  77. I know this question has been asked, but not sure it was answered completely. We had a circulating pump installed but my wife did not want to keep something plugged in that would run 24/7. Someone suggested an Aquastat circulating pump. What is the difference?

    If you had the choice of installing a tankless hot water heater during a renovation which would require additional gas lines or using an Aqustat circulating system, which would you use?

  78. To anyone interested, I ended up removing my Watts pump. After a couple weeks, my water heater sprung a leak. It was 11 years old. My Plumber put in a new heater and advised me to remove the Pump saying that the small increase in pressure that the pump supplied was enough to cause an already marginal tank wall to break down. Water was coming out of both the outlet and inlet pipes and filling the drain pan.

    He said a big part of the reason it was taking so long for hot water to reach my back bath was that the heater was not making hot water fast enough with an internal leak.

    It was taking about 3 minutes for hot water to reach my back bath with or without the pump. After replacing the Heater, I now get hot water in about a minute to a minute and a half. That is about twice as fast as previously. So, I am having mixed feelings about the experience. I am considering selling the pump. The plumber told me that the new tank has check valves in both lines and that they would need to be removed if I were to reinstall the pump. His assessment was that the pump would not really save me any expenses for water and electricity usage.

    So, that is my story. I had to wait three minutes without the pump before to get hot water and then again three minutes wait after the pump. Now I wait half that with no pump. Go figure.


  79. Hi, I wrote the post above on April 8, 2010: “Selecting Domestic Hot Water Recirc Pump – Tankless – no dedicated return line”…and I’m please to report success.

    I now have hot water at the faucets without a dedicated return line using a tankless heater.

    In summary here is what I did:
    – Grundfos Comfort System pump and comfort values (2 of them – one mounted under each of the two sinks on the furthest plumbing “runs” from my tankless.
    – One X10 receptacle, which the Grundfos pump is plugged into
    – One X10 switch in the bathroom and one in the kitchen (to turn on the pump)
    – One relay – which is triggered by the pump turning on, and triggers the tankless (i.e. when the pump is turned on, the relay output goes from Normally Open to Closed. This relay output is connected to the tankless in parallel with the flow switch – so the tankless controller thinks there is >0.5gpm being requested whenever the pump turns on.

    Now when I hit one of the X10 switches in 2-5 mins I have hot water at the faucets without running the water at all. Its not “instant” like some of the other products out there – but unlike those solutions I don’t need power outlet under the sink, and it works for the multiple branches of my plumbing.

    Of course if I had a really regular schedule I could also use my X10 controller to turn the pump on and of at specific times of day… but right now I prefer just hit a button.

    Hope this helps someone… if you want more details post a follow-up.


  80. Response to Anthony;

    With the tankless heating water at below the .5 gpm minimal flow rate aren’t you at all concerned that the system is operating outside of it’s safe perameters? The Grundphos and Watts pumps with the comfort valves obviously prevent flow rates near .5 gpm. But, I am interested in knowing the part numbers you used in your configuration. Could you be specific as the exact x10 devices and the one relay triggered by the pump.

  81. Anthony, it sounds like you have a nice system, but for the benefit of others who would like to copy it, be advised that X10 controls are considered “legacy” devices and should not be used for new designs. If you happen to have a collection of X10 controls lying around, by all means use them, but be aware that as of the mid-2010s their availability is dwindling and some devices have been discontinued. Consider migrating to Insteon from Smarthome.com, or some other remote control technology. Insteon is said to be more reliable than X10, as it uses both house wiring and radio to send signals, and the house wiring signaling is compatible with legacy X10 devices.


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