The part(s) or condition(s) listed below for the symptom Heat pump won't turn off are ordered from most likely to least likely to occur. Check or test each item, starting with the items at the top of the page.
The wall thermostat has electrical contacts that send signal voltage back to the control board and the outside unit's contactor to run the heat pump system. If the contact that controls the contactor sticks closed, it will send continuous voltage to the contactor, causing the system to run continuously. To determine if the thermostat is defective, use a multimeter to test it for continuity. If the wall thermostat shows continuity between the red (“R”) and yellow (“Y”) thermostat wire terminals when the thermostat is in the “off” position, the thermostat has failed and will need to be replaced.
The WiFi thermostat has electrical contacts that send signal voltage back to the control board and the outside unit's contactor to run the heat pump system. If the contact that controls the contactor sticks closed, it will send continuous voltage to the contactor, causing the system to run continuously. To determine if the thermostat is defective, use a multimeter to test it for continuity. If the WiFi thermostat shows continuity between the red (“R”) and yellow (“Y”) thermostat wire terminals when the thermostat is in the “off” position, the thermostat has failed and will need to be replaced.
The control board sends a low voltage signal to the contactor. When the contactor receives the signal from the control board, it closes the circuit, sending voltage to the outside unit components. If the contactor has shorted, it can send continuous voltage to the outside unit's components resulting in the system not turning off. To determine if the contactor is at fault, use a multimeter to test the contactor for a short. If the contactor has shorted, replace it.
If the outdoor coil is clogged with debris, the fan will not be able to move air through the coil, resulting in the coils frosting up faster. The coil can be cleaned with a garden hose and spray nozzle from the inside out. If the coil is excessively dirty, a coil cleaner spray can be used to help loosen the dirt. Inspect the furnace or air handler air filter and replace it with a new one if the filter is dirty or hasn't been changed in the past six months.
If the system is low on refrigerant, the compressor may not be able to heat or cool efficently. This will cause the unit to run longer to maintain the set temperature.
