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heat pump aux heat keeps coming on

What Should You Do When Your Heat Pump’s Aux Heat Keeps Coming On?

Homeowners often find themselves wondering “why does the aux heat keep coming on?” The fact is that your auxiliary heat exists to provide a burst of heat when it is needed. In Arizona, this isn’t something that happens often, but is it bad if the auxiliary heat comes on? If you find that your auxiliary heat is running constantly or you think it is running much more often than it should, you will want to find out what is causing the problem. Here’s what you need to know.

What is Auxiliary Heat?

Auxiliary heat is a feature that is most useful to homes found in milder climates than what you will find in Phoenix. Still, even here, temperatures can get low enough that your heat pump’s auxiliary heat function will kick on to warm up your house quickly to combat a rapidly dropping temperature outside. This, understandably, leads people to ask the question “is it bad if auxiliary heat comes on?”

Typically, heat pumps employ a reverse cycle to maintain the preferred temperature you’ve set on your thermostat. This is the most efficient way to heat homes in warmer climates where the winter temperatures aren’t as persistently low as other areas of the country. However, this process can be slow to do its job, so your auxiliary heat steps into the gap and uses your electric system to give it a kickstart, rapidly turning up the temperature.

Auxiliary Heat Comes On And Stays On

If you are experiencing your auxiliary heat coming on more often than you think it should, you may be wondering how do I stop my auxiliary heat from coming on. There are specific circumstances that can cause your auxiliary heat to kick in and run, some are listed below: 

Temperature Increases

Any adjustment to your thermostat of more than a few degrees can send our auxiliary heat into action. This gets things going while your heat pump catches up. The auxiliary heat will jump in and start bringing the temperature up right away instead of you having to wait. It comes in handy for situations where you’ve set your temperature a little lower, such as while you are at work, and then want to quickly warm it back up once you arrive home. 

Sudden Drop in Temperature

If there has been a sudden drop in the outdoor temperature, it may be hard for your heat pump to do its job alone. The auxiliary heat will provide a much-needed assist, providing some extra power to get quick warmth into your home. This isn’t often necessary in weather above freezing, but in instances where the temperature dips toward 35°F or less, you may see the auxiliary heat kick in to help.

Frozen Heat Pump

The majority of heat pumps contain sensors to detect frozen coils. If there is a problem of this nature, the unit will go into defrost mode. The hot air inside your home will be redirected to frozen components to thaw them. In this event, the auxiliary heat can engage to help keep your home warm while part of its resources is being used to heat the part of the system in need. Some heat pumps will have an indicator that lets you know if this is occurring. This isn’t something you are likely to see much in the Phoenix area, but it’s possible if the weather becomes particularly frigid with snow and ice.

Heat Pump Emergency Mode

There is an emergency setting on most heat pumps. If this is engaged, the auxiliary heat will come on. Sometimes, this happens by accident and you can just turn it back off. If you turn it on for a good reason, let it run for as long as you need it, but you should try to limit it. If you are having to run it too often, you likely have other issues that need to be addressed.

Auxiliary Heat Malfunctions

If your auxiliary heat hasn’t come on for one of the reasons listed above or you can’t figure out why your auxiliary heat has come on, there is a problem that you need to have addressed by a licensed professional. When deciding is it bad if the auxiliary heat comes on, you need to consider why it has come on and if it should be. The signs that you need to request a service call are as follows:

Auxiliary Heat is On but There is No Heat

If your auxiliary heat has turned on but no heat is coming through, there is a problem with your system. There is likely something wrong with the auxiliary system itself because it is not operating as intended. Turn your system off and call for an HVAC technician to come out and make repairs.

Auxiliary Heat Comes On And Stays On

Your auxiliary heat is a backup function. It should rarely run. If the heat pump auxiliary heat is always on there is a problem. If you find that it is running constantly, it may be stuck or not receiving proper signals. You will need to request an inspection and repairs.

Excessive Electricity Bills

You may have many appliances within your home space that waste electricity, but your HVAC unit is one of the biggest consumers of power. If your auxiliary heat is running constantly, it is pulling even more power than is necessary and driving up your energy costs. This can add up over the winter months if you don’t have it addressed.

Auxiliary Heat on Instead of AC

If your auxiliary heat is kicking on in the middle of the summer when your air conditioning is running, this is a serious problem. There is no reason why this should happen, so if it does, you’ll want to turn off the system and request service.

Thermostat Changes Don’t Engage Auxiliary Heat

If you change your thermostat by more than a few degrees and your auxiliary heat doesn’t kick in, there is a problem that will require service.


If you’re wondering how to stop your auxiliary heat from coming on, the information above should help clear it up. If you experience any of the issues listed, your system will need to be serviced. You should not hesitate to have your system inspected and repaired if you think there is a problem with the auxiliary heat. Failure to do so can result in increased energy bills and possible system failures, so contact American Home Water and Air for any issues and we can handle it for you.

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