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Heat pumps are a great way to heat your home, save money and reduce your carbon footprint. However, these energy-efficient systems are complex, require regular maintenance, and can sometimes malfunction or not work as people expect.

At SmartHomePerfected we always advise readers not to undertake any work they are not competent in performing and if in any doubt, it is best to seek the assistance of a professional.

Heat Pump continues to run, after reaching the set temperature

1. Blower Fan set to On

It may not be the heat pump that continually runs after the set temperature is reached. It may be the blower fan within the air handler that continues to run, sending air through the ducts.

You can check the fan setting on your thermostat. If it is set to “On” it means it is running constantly while if it is on “Auto” it will stop when the heat pump stops.

Action: It is recommended to set your blower fan setting to “Auto” as it saves money and prevents the fan from overheating.

2. Blower Relay Switch has Malfunctioned

The controller for the blower fan may be malfunctioning resulting in communication from the thermostat not getting through. This would mean the fan would continue to run even though the heat pump has switched off.

Action: Try to turn off the fan at the thermostat. If it does not work you may need to replace the blower relay.

3. Set Temperature Threshold Never Reached in Cold Weather

Unlike furnaces that pump out high temperatures in short spaces of time, heat pumps generally circulate a warm steady stream of air to gradually increase the temperature of your home.

For that reason, during winter, heat pumps can run for long periods which is completely normal. Once the set temperature is reached, it turns off until the temperature drops below the set temperature when it restarts. 

Some thermostats will attempt to overshoot the set temperature by a degree before turning off and also restart after it has dropped a degree below the target. This is to avoid the system “short-cycling” (frequently turning on and off) which can damage the equipment in the long run.

Very cold weather

Where the external temperature is below 30º F (-1º C), there may not be enough heat in the outside air to warm the refrigerant within the heat pump.

In this scenario, the heat pump alone may not be able to achieve your set temperature, particularly if it is set high. That is where the auxiliary heat source kicks in. 

It cycles on and off to give the extra boost needed to bring the home up to temperature. During this time, the heat pump will constantly run providing as much heat as possible. If the auxiliary heat source switches off before the set temperature (plus the threshold) is reached, the heat pump will keep running trying to achieve it.

Action: Reduce the thermostat setting to test if the heat pump turns off at a lower temperature. Give it a few hours as things move slower when dealing with heat pumps

4. Inspect the Thermostat Wiring

If the message is not getting to the Heat Pump to deactivate on reaching the temperature, it may be down to frayed wiring. The best practice here is to isolate the circuit, remove the faceplate and inspect the wiring to ensure everything is properly connected.

Action: Visually inspect

5. Replace Thermostat Batteries

Some thermostats, without a C-Wire, are powered by AA or AAA batteries. When those batteries run low, there may not be enough power to call the heating system to deactivate.

In this scenario, it is best to replace the batteries. We have a guide on how to replace the batteries here. If you have the Nest thermostat and are running into batteries issues, you can also get instructions here.

Action: Replace batteries

6. Heat Pump Auto-Switching from Heat to Cool to Maintain Temperature

Some Heat Pumps have an auto-reverse mode which allows the system to automatically switch between Heating and Cooling. If the heat pump continues to run after the set temperature has been exceeded, it may be circulating cool air to bring it back in line.

Action: Review thermostat settings

7. EM Heat

It may be possible the emergency heat setting has been activated on your thermostat. This disables the primary heat pump source and relies exclusively on the auxiliary heat source. This could be coupled with another issue such as a failed defrost cycle to cause the issue.

Action: Inspect thermostat. Arrange an inspection and service if other issues

Heat Pump continues to run, without reaching the set temperature

1. Clogged Air Filter or Snow Drift on Outdoor Unit

Heat Pumps need a constant supply of fresh air for the refrigerant to condense or evaporate in order to provide warm or cool air. If the indoor or outdoor filters are clogged, the heat pump will need to work extra hard to achieve the set temperature. If very clogged, it may never achieve it resulting in it constantly running.

Indoor air filters should ideally be changed every three months.

Action: Inspect and clear outdoor filter. Replace indoor filter

2. Heat Set Too High during cold weather with No Auxiliary Heat Source

There is a maximum temperature a heat pump can realize when the outside temperature gets below 30º F (-1º C). If you have your thermostat set higher than this temperature (e.g. 80 °F / 27º C), then it is impossible for the heat pump to reach it. In this case, it will constantly stay on.

Action: Reduce set temperature

3. Heat Set Too Low during hot weather

As above, there is a limit to how low a heat pump can bring down the temperature of a home. If the temperature is set too low, the heat pump will stay constantly on, trying to achieve the temperature.

Action: Increase set temperature 

4. Tripped Circuit Breakers

Have any of the breakers tripped on your board? If so, some of your HVAC equipment may not be running causing the issue. Circuits trip for a reason, so if this is the problem it may be time for a service and investigation.

Action: Check your breaker panel. Arrange a service

5. Windows / Doors Open or Poor Insulation

If your home is drafty, then the air coming through your ductwork will be lost before ever achieving the set temperature on the thermostat.

Action: Close your windows and doors!

6. Refrigerant Leak

If your heat pump is running constantly and is failing to reach the set temperature, there may be a refrigerant leak. This would require a professional service to inspect and resolve the problem.

Action: Check air coming through vents to see if it is cold (when it is set to hot). Inspect coils and compressor. Arrange an inspection and service if confirmed.

7. Damaged Compressor Contactor

If due to wear and tear our compressor contactor is malfunctioning, your heat pump could run continuously without providing air conditioning.

Action: Arrange an inspection and service

8. Malfunctioning or Unplugged Condensate Pump

Heat pumps set to cooling mode produce water as a byproduct of air conditioning. This water either runs off into a floor drain or is collected and removed using a condensate pump via a discharge tube. If your condensate pump is switched off or malfunctioning, it can result in your heat pump continually running.

Action: Visually inspect. Plug in condensate pump if unplugged.

9. Failed Defrost Cycle

It is normal for the external coil on your heat pump to have an icy build-up, as the outside air condenses on the coils. This is why heat pumps have a standard defrost cycle, which reverses the refrigerant to burn off the ice. If you inspect your outside coils and there is a large build-up of ice, it looks like the cycle has malfunctioned. In this case, you can try to reset the system breakers, or more likely you will need to call in the professionals.

Action: Visually inspect and if iced up, power cycle the equipment

10. Stuck in AC mode

Heat pumps contain reversing valves to switch between heating and cooling. If one of these valves gets stuck, the heat pump will continually run, never reaching its temperature.

Action: Check air coming through vents to see if it is cold, with the thermostat set high. If so, arrange an inspection and service

11. Undersized Heat Pump or Ductwork

If a small heat pump is trying to warm up or cool down a large home, it simply might not be up to the job. In this case, the heat pump will continually run without ever hitting the set temperature.

Action: Review heat pump specification vs floor space of home


At SmartHomePerfected we always advise readers not to undertake any work they are not competent in performing and if in any doubt, it is best to seek the assistance of a professional.

Conclusion

We hope this troubleshooting guide helps you to track down and resolve your heat pump issues. Leave a comment if any of these worked or if you have other ideas to add to the list!

Sources

Tempstar

Show CommentsClose Comments

3 Comments

  • Joven Ruthford
    Posted July 29, 2021 at 5:00 pm

    Heat Pumps need a constant supply of fresh air for the refrigerant to condense or evaporate in order to provide warm or cool air. If the indoor or outdoor filters are clogged, the heat pump will need to work extra hard to achieve the set temperature.

  • Rosie m Kenebrew
    Posted December 9, 2020 at 4:42 am

    when its below 30 degrees out side does the out side unit suppose to frost over or not. that makes it run longer is that okay.

    • Daniel Walsh
      Posted December 9, 2020 at 4:49 am

      Hi Rosie,

      During cold temperatures, it is normal for some level of frost to build up on the outside unit. Heat Pumps have a built in defrost cycle for this very purpose so I would recommend you keep an eye on it over a few days. Heat Pumps generally run longer in winter time anyway so that isn’t necessarily an issue.

      If there is a significant build up of ice on the unit, the entire unit is frozen over and air is not being pulled into it then that is a problem. The defrost cycle may be broken, blocked air filters or a number of other potential causes which would need troubleshooting by a HVAC professional.

      Hope this helps

      D

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