Why Is My Heat Pump Not Working? 6 Symptoms and What to Check

Before you start, Lennox's owner guide gives a short pre-service list: check the thermostat settings, make sure all electrical disconnect switches are ON, look for blown fuses or tripped breakers, make sure the unit's access panels are in place, and check that the air filter is clean (Lennox heat pump User Guide). It also says to write down the unit's model number before you call for service. The same guide warns to turn the power off at the disconnect switch before any maintenance.

1. The heat pump won't turn on at all

Start at the thermostat. Make sure it is on Heat (or Cool in summer) and set a few degrees past the room temperature. If the screen is blank, replace the batteries if it uses them. If your thermostat shows a delay message instead, our guide to what "Waiting for Equipment" on a thermostat means explains the built-in wait.

Next, check the switches. Many systems have a disconnect switch near the outdoor unit and a separate power switch for the indoor air handler. Lennox lists all electrical disconnect switches being ON as a pre-service check.

Then check the breaker panel. Here the makers give different advice, and we think you should know both. Bryant says you can reset a tripped breaker once by moving it fully to Off and then back to On, and that if it trips again, you should leave it off and contact a qualified HVAC professional (Bryant heat pump not heating guide). Trane is more cautious: if the breaker has tripped, it says to call for repair, because resetting the breaker and restarting the unit could cause damage (Trane heat pump not cooling guide). Our reasoning: a single reset is reasonable if nothing smells hot or looks burned, but a second trip means stop.

Trane's troubleshooting hub adds that if a heat pump won't turn on or off, the thermostat may not be relaying its signal, and the first step is to have the power source checked by an HVAC professional (Trane heat pump troubleshooting).

2. It runs, but the air feels cool on Heat

Check the fan setting first. Bryant says the thermostat should be on Heat with the fan on Auto. If the fan is on On, the blower keeps running when the heat pump is not heating, which can make the air from the vents feel cool. Our guide on whether your AC fan should be on or auto covers the trade-offs.

Also know what normal feels like. Lennox explains that heat pumps heat a home by delivering large amounts of warm air, which is quite different from furnaces that deliver lower volumes of much hotter air (Lennox HPX15 Homeowner Manual). So air that feels warm rather than hot at the register is not a fault on its own.

Then check the filter. Lennox says to check the indoor filter monthly and clean or replace it as needed. ENERGY STAR says to change filters once a month, and that airflow problems can reduce a system's efficiency by up to 15 percent (ENERGY STAR maintenance checklist). Our guide on how to tell if your furnace filter needs changing applies to air handler filters too.

3. Steam, a stopped fan or frost on the outdoor unit

This one is usually normal. Lennox says frost forms on the outdoor coil when it is heating and outdoor temperatures are below 45°F (7°C), and an electronic control runs a defrost cycle lasting 5 to 15 minutes to clear it. Steam rising from the outdoor unit during defrost is normal, and the thermostat may turn on auxiliary heat during that time.

Bryant describes the same thing from inside the house: during defrost the outdoor fan can stop spinning, steam can rise from the unit, and the system may blow cooler air indoors until defrost ends.

4. Thick ice that doesn't clear

Thick, solid ice that stays after a defrost cycle is not normal. Bryant says that if heavy ice remains after defrost, the system may have a defrost, airflow or mechanical problem that needs a professional, and not to chip at the ice. Lennox says to turn the system off at the thermostat, clear about 2 feet around the unit, check the filter, and never pour hot water on it (Lennox frozen heat pump guide). Our full guide on ice on your heat pump shows how to tell frost from a freeze-up.

5. It stopped after a power outage

Wait before you switch back to normal heat. Lennox says the heat pump has a compressor crankcase heater that protects the compressor in cold weather. If power has been off for several hours or more, set the thermostat to Emergency Heat for temporary heat without risking serious damage. After a six-hour compressor crankcase warm-up, you can switch back to Heat.

In Emergency Heat, all heat comes from the backup heater and the heat pump is locked out, Lennox notes, so expect higher bills if you leave it there.

6. It isn't cooling in summer

The same unit cools in summer, so many checks repeat. Trane says to set the thermostat to Cool with the temperature below the room temperature, set the fan to Auto, keep at least two feet clear around the outdoor unit, and replace or clean filters. Trane also says the only reason a heat pump would be low on refrigerant is a leak, and to call an HVAC company to stop the leak and recharge it. If the unit is more than 10 years old and needs frequent repairs, Trane suggests thinking about replacement.

Sounds that mean stop and call

Some problems are not do-it-yourself jobs. Trane lists banging, screeching, rattling, buzzing, grinding and gurgling as not-normal heat pump noises that can be a sign of electrical issues or system failure, and says to always contact an HVAC professional. Bryant says not to measure refrigerant pressure or work on electrical parts yourself.

Simple upkeep that prevents most calls

• Keep the outdoor unit clear. The Department of Energy says to clear weeds and debris so air can flow freely around outdoor heat pumps (DOE Consumer Guide to Home Heating and Cooling). Lennox adds to keep snow below the unit's louvered panels in winter.
• Check the filter monthly. Both Lennox and ENERGY STAR say to check or change it monthly.
• Book two tune-ups a year. Lennox says the system should be inspected by a licensed technician twice a year, before the cooling and heating seasons.

When to call a pro

Call a licensed HVAC technician if the breaker trips again, if you hear banging or grinding, if thick ice stays after defrost, if you suspect a refrigerant leak, or if the safe checks above don't fix it. Have the model number from the unit's label ready, as Lennox suggests.