Problem with Noise from Tankless Hot Water Heater

I have sounds coming from our tankless water heater. Should I be concerned? -Nora

Hi Nora,

Gas tankless hot water heaters all make noise when firing up and heating water, but the levels are usually less than 90 decibels. A decibel meter can be used to find out how loud your tankless water heater actually is. If you have a smartphone, you can download a free decibel meter app called SoundLevel and measure the decibel output yourself.

If the noise occurs when hot water isn’t being used, there’s a good chance that another source is siphoning water from the line and creating a vacuum. If you hear a weird groaning sound from the pipes or the tankless hot water heater when you flush the toilet, that could be the culprit.

Even though a toilet only uses cold water, I have seen some toilets do this. In that case, you need to have a plumber install a check valve in the water line.

Good luck with your project,


Further Information


  1. Our water heater is considerably noisier than when we had it installed five years ago. Should I have a plumber check it? What could be causing this?

  2. Last night the water was way too hot and I woke up because of the very loud noise the water heater made, it sounded like the system was under high pressure, kind of laud singing pipes . I turned it off. What should I do?

  3. We just purchased a condo. The gas tankless water heater is in the garage and our master bedroom is right on top of it. The water heater makes very loud noise and we couldn’t sleep.

    Is it possible to install a switch to turn it off before we go to bed every night? Thanks.

  4. We’ve had out J-SP199F several years & loved it, now not so much. It has started ‘Growling’ while in use. This is a rumbling growling noise that goes from low tone to louder tone the entire time the hot water is turned on.

    What is causing this & how can we stop it?

    • Hi, Elizabeth,
      Here’s “Today’s Homeowner” host Danny Lipford’s answer to your question:

      “Noise in a tankless water heater can be a result of a variety of issues including improperly set pressure valve, inadequate ventilation, a dirty flow sensor, etc.
      It is definitely something we would suggest you have a pro check out for you.”

      Thanks for writing to us!

  5. We have a Rinnai Thankless water heater. Had been working great when we moved in to house. The last year it has been making a loud vibration and sounds like a jet wanting to take off. Worried it would explode. Have had 5 different AC company’s come and they call the Rinnai service line, but no one has yet been able to find the problem. The entire unit has been cleaned (cost of $1,200 of work has been done on this and it is still happening!) Any suggestions? DB

  6. I have had a few tankless heaters grumbling and banging to the point of shaking walls…pretty scary….I get called in usually after 3 or 4 plumbers have tried to find the issue for repair….I found that the exhaust was covered outside and when moving the weeds/plants away all the noises and banging stopped…the slightest amount of backpressure on the exhaust will ‘choke’ the unit inside when heating….honestly I just stumbled upon this by accident but it has paid off since

  7. Rick – appreciate the comment, you were spot on. I have shelves on the outside of the house below the heater exhaust and an item was partially blocking it. As soon as I moved it the noise stopped. Thank you!

  8. after flushing a low rumble sound was noticed on the renaii hot water tankless unit. I believe it was simply siphoning the water due to being cold and off for a while. it took a couple minutes, but went away. the super tech I talked to believes its the blower. you pick.

  9. Rinnai TS6600

    Makes a constant humming noise when the recirculation pump is on. The installer said it is vibrations in the pipes. However, the humming noise continues even when one or two faucets are open. Driving me nuts, especially in the mornings!

    HELP! Thanks.


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