Heat pumps are extremely efficient and a great way to reduce your carbon footprint. The one issue is that they can be more prone than other HVAC units to having various issues since they are used throughout the majority of the year instead of only in summer or winter. In this article, we’ll look at some of the most common heat pump issues to help you know when you need to schedule an inspection and have your heat pump repaired or replaced.

1. Heat Pump Won’t Run

A heat pump that suddenly won’t turn on is obviously an issue, and this most often happens due to an electrical problem or a problem with the thermostat. If your thermostat registers a temperature where it should be calling for the heat pump to run, the first thing to check is if the circuit breaker is tripped. If the breaker is tripped and you reset it, you can then check to see if your heat pump now comes on. If the unit runs without any issues, it most likely means the breaker tripped due to a sudden power surge. If this is the case, you probably have nothing to worry about.

If the breaker isn’t tripped, you should then check the thermostat. You can try turning the temperature up by five degrees if it is in heat mode or down in cool mode to see if the heat pump comes on. If it starts up, it means that you need to have a technician inspect the unit and recalibrate the thermostat.

If adjusting the temperature doesn’t work, try switching to the opposite mode of what you’re currently trying to use, i.e. from cool to heat or heat to cool. All heat pumps have a reversing valve that allows them to switch modes and reverse the refrigerant flow. If the heat pump turns on when you switch modes, it means the reversing valve is stuck or broken.

If you still can’t get your heat pump to come on, try to turn the fan to “On.” If the blower comes on, you know your thermostat is working. If the blower doesn’t come on, you’ll need to have the thermostat, heat pump, and control board inspected. The thermostat could have failed or there may be an issue like a bad wire or worn-out contactor relay switch that is preventing the heat pump from receiving the signal to run.

Another possibility is that the start capacitor is bad. The start capacitor provides an extra surge of electricity to help the condenser fan motor and compressor motor start. If the start capacitor is bad, the heat pump generally won’t ever run as it doesn’t have enough power for the motor to start. A bad start capacitor can also lead to the circuit breaker constantly tripping every time the heat pump tries to run. With a bad start capacitor, you will hear a repeated clicking sound coming from the heat pump when it attempts to turn on.

2. Heat Pump Won’t Heat

This issue is quite similar to the one we just discussed. If your heat pump suddenly stops producing heat or suddenly won’t turn on in heat mode, it almost always indicates an issue with the reversing valve. Whenever a heat pump needs to defrost, it activates the reversing valve and temporarily switches to cool mode so that hot refrigerant flows back outside and through the coil. Sometimes the valve can malfunction or get stuck, which will prevent the heat pump from switching back to heat mode at the end of the defrost cycle. This issue can also happen when you try to run your heat pump on heat mode for the first time in the winter and it won’t turn on.

3. Heat Pump Is Frozen and Won’t Defrost

Ice will always build up inside a heat pump whenever it runs in cold weather. Most heat pumps have a temperature sensor inside them. When the sensor detects that the coil is too cold and starting to freeze, it will signal the heat pump to run in defrost mode. However, some units just have a timer that will switch them to defrost mode at set intervals instead.

It usually takes no more than 15 minutes for a heat pump to defrost. If you ever notice your heat pump is frozen for more than an hour or two, you can try to force it to defrost. All you need to do is switch the thermostat to cooling mode. If the unit doesn’t immediately come back on or is still frozen after running it in cooling mode for an hour or so, it’s usually an indication that you need to have the reversing valve repaired or replaced.

4. Thermostat Is Always on Auxiliary Heat Mode

In colder climates, all heat pump systems need an auxiliary source of heating. Most systems have electric heat strips mounted in the air handler that function as the auxiliary heat. The auxiliary heat will always automatically come on when the heat pump starts defrosting. If this doesn’t happen, the temperature will quickly start dropping since the heat pump pulls heat out of the building when defrosting. If the home is more than a few degrees cooler than the desired temperature, the thermostat will also switch on the auxiliary heating. In this case, both the auxiliary heat and the heat pump will function together to raise the temperature more quickly.

When the auxiliary heating is on, the thermostat will always show “Aux” or “Aux Heat.” There is really only one situation when the thermostat should constantly show Aux mode if your heat pump is working properly, and that is if the outdoor temperature is well below zero. In extremely cold weather, the heat pump won’t be able to work effectively. This means the thermostat will keep the auxiliary heating running constantly.

If your thermostat stays in Aux mode for a long time and the temperature isn’t that cold, you should go outside and see if the heat pump is frozen. If the unit is frozen, it means, again, that there’s an issue with the reversing valve. If the heat pump isn’t frozen, you should also check to see what temperature the thermostat registers. If the temperature is more than three degrees cooler than it should be, the thermostat should switch out of Aux mode as soon as your home reaches the right temperature.

If the thermostat doesn’t switch back to normal heat mode when it registers the correct temperature, it means that either your heat pump won’t turn on or isn’t working effectively. If the heat pump isn’t working effectively enough to prevent the temperature from dropping, the thermostat will either constantly run in Aux mode or constantly keep switching back to it anytime the temperature again starts decreasing.

5. Unusual Sounds

Unusual sounds like rattling, humming, buzzing, screeching, grinding, hissing, etc. are all definitely signs that you need to have your heat pump inspected. Some of these sounds can be a sign of an extremely serious problem or could lead to severe problems and major damage. As such, we recommend turning your heat pump off if it starts making any unusual sounds until you have a technician inspect it. If you leave the unit running, you may run the risk of it burning out.

With more than four decades of experience in the HVAC industry, Endless Energy is the place to turn to for all of your heating and air conditioning needs. We offer expert heat pump services as well as home energy assessments and insulation services, and we serve customers in Marlborough and throughout Massachusetts. If you need to have your heat pump inspected or any other HVAC service, contact us today.

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