The part(s) or condition(s) listed below for the symptom Heat pump not heating 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.
A run capacitor stores and releases a charge to start and run the condenser fan motor. If the capacitor is defective, the fan motor might be noisy, overheat, or not run at all, resulting in the unit not heating. To determine if the run capacitor has failed, inspect the capacitor. If the dual run capacitor is bulging or leaking, replace it.
A dual run capacitor stores and releases a charge to start and run both the compressor and the condenser fan motor. If the capacitor is defective, the fan motor might be noisy, overheat, or not run at all, resulting in the unit not heating. To determine if the dual run capacitor has failed, inspect the capacitor. If the dual run capacitor is bulging or leaking, replace it.
To determine if the condenser motor is working, use a multimeter to test the incoming voltage to the motor. If the condenser fan motor is receiving the correct voltage but the motor still won’t run, inspect the capacitor to ensure that it is not at fault. If the capacitor is not bulging or leaking, replace the condenser fan motor.
Since the blower motor is the component that circulates the heated air through the home's venting, a defective blower motor will result in the unit not heating. You can use a multimeter to test the blower motor for electrical continuity, a continuous electrical path present in the motor, as well as determine if power is reaching the motor. You can also try turning the blower wheel by hand. If the wheel does not turn freely, it's likely the motor bearings have seized and the blower motor will need to be replaced.
Since the circulation blower fan motor is the component that circulates the heated air through the home's venting, a defective motor will result in the unit not heating. You can use a multimeter to test the motor for electrical continuity, a continuous electrical path present in the motor, as well as determine if power is reaching the motor. You can also try turning the blower wheel by hand. If the wheel does not turn freely, it's likely the motor bearings have seized and the motor will need to be replaced.
The air handler 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 is defective, it will not provide voltage to the outside unit. To determine if the contactor is at fault, use a multimeter to test the contactor for continuity. If the contactor does not have continuity, replace it.
As the outdoor temperatures get colder, the outdoor coils can start to freeze up more often. When the coils frost up, a defrost control board or thermostat will energize a reversing valve to divert the warmer refrigerant from the indoor coil to help melt the excess frost from the outdoor coil. If the defrost thermostat is defective, the frost on the outdoor coils may be unable to melt. To determine if the defrost thermostat is defective, use a multimeter to test it for continuity. If the defrost thermostat does not have continuity when it reaches the low temperature of its operating range, replace it.
Heat pumps have a reversing valve that can reverse the direction of the refrigerant through the condenser and evaporator coils when heat is required. This will effectively make the condensing coils behave like an evaporator, and the evaporator coils behave like a condenser. The heat that is dissipated when the unit is in its cooling mode will, instead, be used to warm the air in the room. If the reversing valve is faulty and unable to reverse the direction of the refrigerant, the unit may be unable to heat.
A temperature sensor monitors the temperature of the outdoor coils. If the coils begin to frost over, the sensor will alert the defrost control to allow power to energize a reversing valve to divert the warmer refrigerant from the indoor coil to the help mel the excess frost from the outdoor coil. If the temperature sensor is defective, the defrost system will not be alerted to the excess frost.
If the outdoor coil is clogged with debris, the outdoor fan will not be able to move air through the coil, resulting in a loss of heating. 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.
As the outdoor temperatures get colder, the outdoor coils can start to freeze up more often. When the coils frost up, a defrost control board or thermostat will energize a reversing valve to divert the warmer refrigerant from the indoor coil to help melt the excess frost from the outdoor coil. If the defrost control board is defective, the frost on the outdoor coils may be unable to melt. Before replacing the defrost control board, first confirm the reversing valve and defrost thermostat are functioning. If the reversing valve and defrost thermostat are working properly, the defrost control board is likely defective.
The compressor is a pump which compresses the refrigerant and circulates the refrigerant through the evaporator and condenser coils. If the compressor is not working, the unit won’t heat. However, this isn’t usually the case. Before replacing the compressor, first check all of the more commonly defective components. If all of the other components are working properly, use a multimeter to test the compressor for continuity. If there is an open circuit, the compressor is likely defective. If the compressor is defective, it must be replaced by a licensed technician.
The control board sends a low voltage signal of 24 volts to the contactor through the wall thermostat. When the contactor receives the signal from the control board, it closes the circuit, sending voltage to the outside unit components. There should be 24 volts between the common (“C”) and yellow (“Y”), and common ("C") and orange ("O") thermostat wire terminals on the air handler control board when the wall thermostat is in the heating mode. You can check for this voltage with a multimeter. If voltage is not reaching the contactor or reversing valve, it's likely the wall thermostat is defective and will need to be replaced.
The control board sends a low voltage signal of 24 volts to the contactor through the WiFi thermostat. When the contactor receives the signal from the control board, it closes the circuit, sending voltage to the outside unit components. There should be 24 volts between the common (“C”) and yellow (“Y”), and common ("C") and orange ("O") thermostat wire terminals on the air handler control board when the WiFi thermostat is in the heating mode. You can check for this voltage with a multimeter. If voltage is not reaching the contactor or reversing valve, it's likely the WiFi thermostat is defective and will need to be replaced.
If the unit has good air flow, the evaporator and condensing unit coils are clean, the fan and compressor are running, and the furnace or air handler blower is on, but there is still not enough heating, it is likely there is a leak or restriction in the sealed system. Since diagnosing and repairing a sealed system takes specialized tools and knowledge, a qualified service technician should diagnosis and repair the unit.
The control board regulates the power supply to all of the components of the furnace or heat pump system. If the control board fails, it might not send voltage to the ignition system, causing the unit not to heat.
The control board sends a low voltage signal of 24 volts to the contactor. When the contactor receives the signal from the control board, it closes the circuit, sending voltage to the outside unit components. Some air handlers have a separate transformer for the 24 volt circuit, so if the contactor is not receiving the proper voltage, it's likely this transformer has failed and the component will need to be replaced.
The main control board regulates the power supply to all of the components of the furnace or heat pump system. If the control board fails, it might not send voltage to the ignition system, causing the unit not to heat.
The outdoor unit is energized with 240 volts of electricity. The electricity flows through a disconnect box to the compressor and outdoor fan motor. The disconnect box enables the outdoor unit to be turned off outside. The disconnect box includes a cartridge which may contain fuses. If the compressor and condenser fan motor do not run, the disconnect box fuses may have blown, or the circuit breaker that supplies power to the disconnect box may have tripped. To determine if the disconnect box fuses have blown, use a multimeter to test the fuses for continuity. Fuses that do not have continuity should be replaced.
For the heat pump to work properly, the wall thermostat should be set for "Heat" and the fan set for "Auto" or "Fan On". The temperature setting also needs to be set higher than the room temperature. When the thermostat is set properly, both the outdoor unit and the furnace or air handler blower should be running.
