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Heat Pump Blower Runs Continuously? – Here’s Why

If your heat pump blower runs continuously, first make sure whether it’s reaching the desired temperature or not. If it is, the problem could be your thermostat or the blower relay switch.

If it isn’t reaching the desired temperature, it could be extremely cold weather, a sign of low refrigerant, a bad compressor, or another type of internal problem.

Why your heat pump blower keeps running after reaching the desired temperature

Thermostat issues

Problems with your thermostat can also cause your heat pump blower to continue running.

  • One of the most common causes is the “Fan” switch being put in the incorrect position. It typically has two options—“Auto” and “On.” You want it to be on “Auto.” Otherwise, the fan will run continuously.
  • Ideally, you should set your thermostat to “Cool” mode in summer and “Heat” mode in winter. This will prevent your thermostat from automatically switch between “Cool” and “Heat.”
  • A newer thermostat may have another fan setting called “Circ,” which is short for circulation. This tells the fan to kick back on periodically even when there isn’t a demand for cooling just to circulate the air.
  • If your thermostat’s batteries are low, it could behave unexpectedly. One result of that might be that your heat pump blower starts running when it shouldn’t.
  • If your thermostat’s wiring was done incorrectly, it may send incorrect messages to your heat pump. That could cause heat pump blower malfunctions as well.

Blower relay switch malfunction

Your blower motor is controlled by a relay switch. When this malfunctions, the fan often runs continuously. You’ll need to replace this faulty switch if that’s what you think your problem is.

Why your heat pump blower keeps running without reaching the desired temperature

Before doing anything, make sure your airflow is not restricted. You may need to inspect your filters, supply vents and air registers. Also, air leaks in ducts can reduce the heating or cooling capacity of your heat pump.

If you think your thermostat is not reaching the set temperature, you may need to check your thermostat’s calibration and its wiring. Also, the thermostat location is important in determining the accuracy of readings.

Extreme cold weather

Heat pumps aren’t efficient in extremely cold weather. That’s why many homes have an auxiliary heating system for these situations.

But if your blower keeps running, it could mean that your heat pump isn’t switching to the backup system correctly. This makes it seem as though the blower fan keeps running because it needs to stay on longer to heat your home.

To see if this is the problem, bring down your thermostat setting for a few hours. See if the fan turns off when you do that. If it does, it’s a sign that this could be your problem.

Also, you can go outside and verify that your heat pump condenser is running. If it isn’t, take a look at the fuses and breakers in its systems. You might need to reset a breaker, but if it trips again, call out a professional to take a look at it.

Just be careful of touching the refrigeration lines going to your heat pump condenser. These can be very hot. But if they’re cold, then you probably have an issue with the refrigeration system of your heat pump.

Low refrigerant

When your system doesn’t have enough refrigerant, it’ll cause low heat absorption. That can lead to a variety of issues, like insufficient heating or cooling. And these can cause your blower fan to misbehave.

Bad condenser fan motor

It’s also possible that your condenser fan motor is the source of your problem. When it gets dirty, broken, or covered with ice, the heat pump struggles with airflow. This can lead to a decrease in heating power.

Faulty compressor

Your heat pump relies on its compressor to transfer heat. When it breaks, so does your system’s ability to efficiently transfer heat. And that can lead to problems with your blower fan.

You may also have a damaged compressor contractor, which controls the amount of power supplied to your heat pump.

Defrost control board problems

Your defrost control board is responsible for thawing accumulations of ice that occur on your condenser. When it doesn’t work, heat transfer is restricted.

As is the case with a faulty compressor, this can also lead to issues with your blower fan down the line.

Issues with reversing valve

Your system also needs a functioning reversing valve to work properly. If it doesn’t have one, then it may do the opposite of what you tell it to do.

For example, you may tell your system to heat your home, but it may go into cooling mode instead. This can cause your blower motor to come on when it shouldn’t as well.

Michael Joseph


Saturday 9th of April 2022

Is it conceivable that a faulty defrost board would run up the electric bill by calling for defrost even in hot weather?

We have a Carrier 25HCD348A310, less than five years old when we moved in. However, the electrical bills were sky-high in summer (nearly a grand a month for 1400SQ late '70s house with newer dual-paned windows).

Suspected that the heat strips were running with the AC but replacing the wiring from the thermostat to the unit only dropped the bill by $100 per month. Meanwhile, still having issues with intermittent 5amp fuse failures. Blower/fan checked out and no visible wiring issues found on 3 separate calls for this issue. That leaves the thermostat (which was replaced when we moved in), the condensor (but the tech thinks the refrigerant lines are plenty cold enough and has yet to check for low refrigerant) and a board failure (defrost board, control board or what?)

We inherited some of the records associated with the previous owner. Looks like they charged her repeatedly almost from the get-go to replace the thermostat every year. On inspection we found the blower working but the condenser wasn't powered (in the wrong position at the panel). Everything seemed to work normally but for the high summer electric bills until the fuses started blowing the following winter. At that time the tech reported that an over-rated fuse was installed (speculating that the prior owner may have had a higher-rated fuse installed to "trick" it into not blowing?)

At any rate, looks like the install was faulty from the time it was put in. In point of fact, the company that installed it for the prior owner went out of business.

Since the fuses are blowing consecutively but then running for six months or a year before they again trip — and since the electric bills did not come down that much — would it be reasonable to suspect a faulty defrost control board (as in the defrost cycle is running year around, needed or not)?