Air Source Heat Pump Keeps Cutting Out

Is your heat pump's heating or cooling out of sync with the temperature setting on your thermostat? Short cycling could be the culprit. Short cycling is when a faulty heat pump system shuts off and restarts too many times or more in a single day.

Here are four common heat pump problems that cause short cycling:

1. Inaccurate Thermostat

Short cycling can be caused by an inaccurate thermostat measuring temperature. When this happens, the heat pump shuts off heating and cooling modes before the set temperature is reached. This problem can be fixed by adjusting the thermostat's heat predictor. This can be done manually by the owner or a trained technician.

Another possible cause is that the thermostat is installed in the wrong location. In order to accurately measure air temperature, the thermostat must be placed away from sunlight, outdoor air, or vents.

2. The Wrong Size of Heat Pump

This is the most expensive problem. Short cycling can be caused by a heat pump that is too powerful or too weak for the specified space. Before installing a heat pump, a trained HVAC technician should perform a heat load calculation (also known as a manual J calculation) in the space where the heat pump is to be installed. The calculation determines the optimum heat pump power output for precise heating and cooling. If an inexperienced technician fails to perform the calculation or performs it incorrectly, an oversized heat pump may be installed.

3. Clogged Air Filters

Heat pump air filters prevent contaminants in the air from being drawn into the system's sensitive working parts. But if air filters are not cleaned at prescribed maintenance intervals, they will eventually clog, resulting in restricted airflow, which can lead to overheating. When heat pumps overheat, they shut down.

Short-cycling caused by overheating can cause serious damage. To avoid this, check air filters at prescribed service intervals and clean or replace as needed. During extremely cold and hot seasons when heat pump usage is high, monthly air filter inspections are recommended.

4. Refrigerant Leaks

The air conditioning or air cooling function of a heat pump is achieved through a process that relies on refrigerant. In cold weather, refrigerant transfers heat from the outdoors, pressurizes it, and then releases it to the indoor space. But when a heat pump leaks refrigerant, the heat pump will short-cycle and fail to adequately heat the space. Ice on an outdoor heat pump unit is a common sign of a refrigerant leak. When ice is noticeable, contact a trained technician as soon as possible.

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