Universal diagnostic library
Heat-pump problems by mode and operating state
Heat-pump problems by mode and operating state: behavior changes with outdoor temperature, thermostat configuration and defrost.
A heat pump that heats poorly or ices up needs a few checks you can do safely: replace a dirty filter, make sure the outdoor unit is clear of snow, leaves and debris, check the thermostat mode and set point, and confirm the breakers are on. A thin layer of frost on the outdoor coil in winter is normal, and the unit clears it with a defrost cycle that may produce steam; thick ice that does not clear is a service call. The reversing valve and the auxiliary heat strips have their own pages.
Heat pump problems: what to check before calling
Heat pumps have a few behaviors that look like faults but are normal. In winter the outdoor unit goes through a defrost cycle every so often, which can send out steam and stop the fan for several minutes, and the indoor air may feel cooler during it. Auxiliary or emergency heat uses electric resistance elements, runs when the heat pump cannot keep up or when you select it, and costs more to run, so a thermostat stuck on emergency heat is worth checking early.
If the heat pump runs but the house does not warm, check the filter, the thermostat mode and set point, snow or leaves around the outdoor unit and the vents inside. A unit that cools when set to heat may have the reversing valve set wrongly on the thermostat or a stuck valve. Ice that covers the whole outdoor coil and does not clear, refrigerant noises and electrical faults are for a licensed technician.
Is steam from my heat pump outdoors normal?
Yes, in cold weather the unit defrosts and the melting frost can produce steam. A thick layer of ice that does not clear needs service.