Heat pumps are the most efficient and least expensive option for heating your home. However, heat pumps can also be more prone to problems since they get so much more use than furnaces. Having your heat pump stop working in winter is a major issue you’ll want to take care of immediately.
We’ll look at some of the most common problems heat pumps can experience in winter, what causes them, and what steps you can take to resolve each one.
Heat Pump Is Frozen
The first thing you need to understand is that it is completely normal for a heat pump to frequently freeze up in winter, and this is especially true in the freezing cold Canadian climate of Belleville, ON.
For a heat pump system to heat effectively, the refrigerant that flows through the outdoor heat pump unit must be much colder than the air temperature. When the refrigerant is so cold, ice will always start forming on the coil in the heat pump whenever the outdoor air temperature is under 7 degrees Celsius.
This issue is why all cold-climate heat pumps have a defrost cycle that will run occasionally to thaw the coil and allow the system to continue heating. Older heat pumps typically have a timer that you can program so the defrost cycle runs at set intervals. Most newer units have a temperature sensor instead; it will automatically trigger the defrost cycle to run when the coil gets too cold.
In order to defrost, a heat pump switches over to cooling mode. This means the system starts capturing heat from inside and pumps hot refrigerant through the outdoor coil to quickly thaw it out. In most cases, it will only take 15 minutes at the most for the unit to fully defrost and then switch back to normal heating mode.
If you notice your heat pump is covered in ice and stays that way for more than an hour or so, it usually indicates that something is preventing it from switching to defrost mode. In this situation, you can try to troubleshoot the problem by switching your thermostat to cooling mode. If it won’t switch modes, you can be fairly certain that the heat pump’s reversing valve is broken or stuck.
This valve is what enables a heat pump to switch between cooling and heating modes. The reversing valve is activated by a solenoid, which can also fail and prevent the valve from operating. A technician should be able to fix the issue quite easily if the valve is just stuck. If the valve or the solenoid is bad, your only option is to have the bad component replaced.
If you can get the system to switch modes but your heat pump still has lots of ice inside it, the problem likely lies with its condensate drain. The condensate drain line can get clogged, which prevents all the water from draining away from the unit when it defrosts. This can lead to ice continually building up inside the unit to the point that it may never fully defrost. This issue can also occur if the drain line doesn’t have enough slope. Without sufficient slope for the water to drain properly, the line can quickly start freezing. This means the water will start backing up and freezing inside the heat pump.
Thermostat Is Constantly in Auxiliary Mode
Cold-climate heat pumps must have some type of auxiliary heating that will kick in during the defrost cycles. The auxiliary heating will also run if your home is much colder than the thermostat setting or if the outdoor temperature is too cold for the heat pump to work. Whenever the auxiliary heating is running, your thermostat will show it is in AUX or AUX HEAT mode.
Most cold-climate heat pumps can function in temperatures as low as -25 to -30 degrees Celsius. If the temperature outside is below this, your thermostat will always show it’s in auxiliary mode since it is too cold for the heat pump to work.
The system will also temporarily run in auxiliary mode anytime your home is more than 2 to 3 degrees colder than the thermostat setting. However, it should switch back to normal heating mode within half an hour once your home is at the desired temperature.
If your home is fully warm and it isn’t too cold for the heat pump to work, your thermostat should never stay in the auxiliary mode for more than 20 to 30 minutes. If it stays in auxiliary mode any longer, it typically means that either the heat pump isn’t running for some reason or that it won’t defrost. This can again be due to an issue with the reversing valve, or there may be an electrical issue that is preventing your heat pump from turning on.
Heat Pump Only Runs for a Short Time and Then Shuts Off
Another fairly common issue is when a heat pump keeps shutting off after only a few minutes. This can happen simply because the unit is too large, which will lead to it constantly short-cycling or only running for a short time. If your heat pump is fairly old, this issue can also indicate that the compressor is wearing out. In either of these cases, the only solution is to replace the heat pump.
Issues with the reversing valve can also lead to a heat pump quickly shutting down not long after starting. A stuck or broken reversing valve will often cause the compressor to quickly start overheating. When this happens, the appliance will automatically shut down to avoid being damaged.
One thing you should always check in this situation is that your heat pump isn’t blocked by snow or debris. If the unit is blocked, it won’t receive proper airflow and may quickly overheat and shut down.
Heat Pump System Blows Cold Air
You may also experience issues where your heat pump system starts blowing cold air in the winter. As with most other heat pump problems, this normally happens due to an issue with the reversing valve. If the reversing valve breaks or gets stuck, your heat pump can get stuck in defrost mode and be unable to switch back to heating mode. If your auxiliary heating fails or won’t turn on, you’ll also notice cold air coming out of the vents whenever your heat pump defrosts. However, the system should start putting out warm air again fairly quickly.
One other possibility is that the coil in the outdoor part of the system is dirty. A dirty coil can prevent the system from absorbing heat. This can lead to the refrigerant staying colder than the temperature in your home, which will make the system put out cold air. Having a technician clean the coil should immediately fix this problem. You can also easily prevent it with twice-yearly heat pump maintenance.
If you experience any of these issues with your heat pump this winter, or your system has any other problems, you can count on our experienced team at Armour Home Comfort for help. We’ve been providing expert heating and cooling services in the Belleville area for more than 30 years, and we’re ready to take care of all of your HVAC repair, maintenance and installation needs.
Give us a call today for a heat pump inspection or any other heating or cooling maintenance service you need!
