Heat pumps have become increasingly popular for their energy efficiency and versatility in both heating and cooling homes. However, like any HVAC system, they can experience issues from time to time. Homeowners may face problems such as the heat pump not cooling or heating properly, leaking water, emitting strange odors, or making unusual noises. 

The good news is that many of these common heat pump problems have simple solutions that you can often address yourself. This guide will explore the most frequent heat pump issues, their causes, and practical solutions to keep your system running smoothly.

Thermostat Issues

Thermostat problems are often the root cause of many heat pump malfunctions. When a heat pump isn’t functioning correctly, the thermostat should be the first component you check. This is especially true for homes with HVAC zoning systems that use multiple thermostats.

Check each thermostat to ensure it is properly set or programmed. You may be having a heat pump thermostat wiring issue. In some cases, especially with modern digital or infrared thermostats, there may be a calibration issue. This latter problem generally requires professional repair due to the complex circuitry involved.

Signs of a Thermostat Problem

Several indicators can point to a thermostat issue:

  • The displayed temperature doesn’t match a separate, working thermometer
  • The display shows the heat pump in one mode (heating or cooling) while the system is operating in another
  • The thermostat shows the heat pump should be on or off, but the system isn’t responding

Using the Fan Switch for Diagnosis

You can use the fan switch as a useful diagnostic tool. By simply turning the fan on, one can quickly determine if the unit has power and if the thermostat’s switch is functioning and sending the proper voltage. It will also tell you if the transformer is relaying the correct voltage and if the indoor fan motor and relay are working properly. 

Fan Problems

When the fan isn’t working, it can lead to inefficient operation and high electricity bills. Various issues can cause faulty fans.

Fan Tripping the Breaker

If the fan is tripping the circuit breaker, it could be due to faulty wiring, a bad blower motor, or a bad control board. You may have faulty wiring, the blower motor could be bad, or the control board may need to be replaced. Damage to the motor or control board will require replacing the component.

Fan Not Starting

If the fan simply fails to start during the fan switch test, the problem likely lies between the thermostat and the fan. Possible causes include a fault in the thermostat, low voltage, or an issue with the fan relay. 

In colder climates, heat pumps often have an additional external thermostat. If the temperature is below this thermostat’s setpoint, the unit won’t run even if the indoor thermostat is triggered. Adjusting the outdoor thermostat’s settings may resolve this issue.

Heat Pump Won’t Start

Discovering that a heat pump won’t start during extreme temperatures can be frustrating. There are several potential causes that homeowners can easily diagnose.

Power Issues

Occasionally, a heat pump may trip the circuit breaker. If this happens frequently, we recommend calling an HVAC technician to check for faulty wiring.

Start Capacitor Problems

The start capacitor is responsible for transmitting an electric charge to start the motor. A clicking noise from the heat pump’s cabinet, when it’s set to start, is a clear sign that the start capacitor needs replacement.

Heat Pump Won’t Stop Running

A heat pump that won’t stop running can lead to system damage and increased energy costs. This issue can cause the indoor coil to freeze in cooling mode, potentially expanding to the outdoor unit.

Compressor Contactor Issues

The compressor contactor in the outdoor unit has contacts that can become pitted over time. These should generally be replaced every few years. Damaged contacts can fuse together, locking the system into its current mode.

Thermostat Cable Short

A short in the thermostat cable can go unnoticed until power stops flowing correctly. This can be caused by:

  • Accidental damage from a weed whacker
  • Being pinched too tightly by a staple
  • Pests chewing on the cable

Once you diagnose it, replacing the damaged cable is a simple fix.

Heat Pump Won’t Switch Between Warm and Cool Air

One of the key advantages of heat pumps is their ability to provide both heating and cooling. When the system gets stuck in one mode, it can be a significant inconvenience.

Damaged Reversing Valve

When the heat pump provides cool air but not hot (or vice-versa), the reversing valve is likely the culprit. This valve controls the directional flow of refrigerant, dictating whether the pump produces warm or cool air. In this situation, you will need to have an HVAC contractor replace the valve. 

Refrigerant Leaks

If the system is only capable of producing lukewarm air, a refrigerant leak may be the cause. This issue requires attention from an EPA-certified HVAC technician who can repair the leak and recharge the refrigerant.

Heat Pump Won’t Cool

When a heat pump fails to cool effectively, it can make a home unbearable during hot weather. Common causes include refrigerant leaks, dirty evaporator coils, or a malfunctioning compressor.

Refrigerant Leak

A refrigerant leak can significantly reduce the heat pump’s cooling capacity. This issue requires professional attention to locate and repair the leak, then recharge the system with the correct amount of refrigerant.

Dirty Evaporator Coil

A dirty evaporator coil can restrict airflow and reduce cooling efficiency. To prevent this, check the HVAC filter monthly and replace it when it’s dirty. Clean the coil regularly with a soft brush and mild detergent solution

Heat Pump Won’t Heat

Common causes of a heat pump not heating include a faulty reversing valve, low refrigerant levels, or a frozen outdoor unit.

Faulty Reversing Valve

As we mentioned earlier, a stuck or damaged reversing valve can leave the system blowing only cold air. This part will need to be replaced by an HVAC professional.

Outdoor Unit Freezing

In cold weather, the outdoor unit may freeze up due to poor defrost cycle control or low refrigerant. You should check that the defrost control is working properly and have an HVAC contractor check refrigerant levels if necessary.

Heat Pump Icing Up

Ice buildup on a heat pump, especially in winter, can significantly impact its performance. This problem typically has two potential causes.

Defrost Controls

Manually starting the defrost mode can help diagnose issues with the defrost controls:

  • For older models, manually advance the defrosting timer motor
  • For newer models, check for pins on the electronic defrost control that can be jumped to initiate defrost mode

Low Refrigerant

Low refrigerant levels can cause icing and must be addressed by a professional. Another symptom of this issue is the unit producing only lukewarm air.

Heat Pump Leaking Water

Water leaks from a heat pump can damage your home and indicate system problems. Common causes include a clogged condensate drain or a frozen evaporator coil.

Clogged Condensate Drain

The condensate drain line can become clogged with debris, causing water to back up and leak. To resolve this, clear the drain line of any debris and make sure the line is properly sloped for proper drainage. 

Frozen Evaporator Coil

A frozen evaporator coil can cause water leaks as the ice melts. To prevent this, check and replace the air filter if dirty and clean the coils if they are caked with dust. 

Heat Pump Smells Bad

Unpleasant odors from a heat pump can be a sign of various issues and‌ affect indoor air quality.

Dirty Air Filter

A dirty air filter can cause the heat pump to emit unpleasant odors. Replace the filter every 1–3 months to maintain good indoor air quality.

Mold Growth

Moisture buildup in the system can lead to mold growth, causing musty smells. To address this, have your ductwork and evaporator coil professionally cleaned and use preventive measures (like dehumidifiers) to control moisture and prevent future mold growth. 

Outdoor Unit Not Turning On

Common causes of the outdoor unit not turning on include a tripped circuit breaker or a faulty contactor.

Tripped Circuit Breaker

Check the electrical panel to see if the circuit breaker for the heat pump has tripped. Reset it and observe if the outdoor unit starts. If it trips again, call an HVAC professional to inspect for electrical issues.

Faulty Contactor

The contactor in the outdoor unit can wear out over time, preventing the unit from starting. An HVAC technician can replace the contactor to restore function.

Short Cycling

Short cycling occurs when a heat pump turns on and off frequently, causing excessive wear and tear on the system. This can be caused by an oversized system or a dirty air filter.

Oversized System

If the heat pump is too large for your home, it will likely short cycle. Have an HVAC professional assess the system size and make recommendations for a properly sized unit if necessary.

Dirty Air Filter

A clogged air filter can cause the system to overheat and short cycle. Replace the filter regularly to maintain proper airflow and prevent this issue.

Making Noises

Abnormal sounds from a heat pump can range from minor annoyances to signs of serious problems. Common causes include loose parts or a failing compressor.

Loose Parts

Rattling or banging noises often indicate loose parts. Tighten any loose screws or bolts, and call a professional if the noise persists.

Failing Compressor

A buzzing or humming noise may signal a failing compressor. This serious issue requires immediate attention from a qualified HVAC technician.

Final Thoughts 

Heat pump issues can be frustrating, but many common problems have straightforward solutions. By understanding these issues and their causes, you can often diagnose and sometimes resolve problems on your own. 

Regular maintenance, such as changing air filters and keeping the system clean, can prevent many issues from occurring in the first place. However, for complex issues or those involving refrigerant or electrical components, it’s best to call a qualified HVAC technician.

Frequently Asked Questions

Why is my heat pump blowing cold air in heat mode?

It likely has a faulty reversing valve or low refrigerant levels. Contact an HVAC professional for diagnosis and repair.


How often should I have my heat pump serviced?

Schedule annual maintenance (once a year) with a qualified HVAC technician to keep your system running efficiently and catch potential problems early.


Why does my heat pump keep tripping the circuit breaker?

A heat pump that repeatedly trips the breaker may have a faulty compressor, wiring issues, or an overloaded circuit.


Editorial Contributors
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Henry Parker

Henry Parker is a home improvement enthusiast who loves to share his passion and expertise with others. He writes on a variety of topics, such as painting, flooring, windows, and lawn care, to help homeowners make informed decisions and achieve their desired results. Henry strives to write high quality guides and reviews that are easy to understand and practical to follow. Whether you are looking for the best electric riding lawn mower, the easiest way to remove paint from flooring, or the signs of a bad tile job, Henry has you covered with his insightful and honest articles. Henry lives in Florida with his wife and two kids, and enjoys spending his free time on DIY projects around the house. You can find some of his work on Today’s Homeowner, where he is a regular contributor.

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Jonathon Jachura

Contributor

Jonathon Jachura is a two-time homeowner with hands-on experience with HVAC, gutters, plumbing, lawn care, pest control, and other aspects of owning a home. He is passionate about home maintenance and finding the best services. His main goal is to educate others with crisp, concise descriptions that any homeowner can use. Jon uses his strong technical background to create engaging, easy-to-read, and informative guides. He does most of his home and lawn projects himself but hires professional companies for the “big things.” He knows what goes into finding the best service providers and contractors. Jon studied mechanical engineering at Purdue University in Indiana and worked in the HVAC industry for 12 years. Between his various home improvement projects, he enjoys the outdoors, a good cup of coffee, and spending time with his family.

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