Heat Pump Not Heating? What to Check Before You Call

Start at the thermostat. Make sure the mode is Heat or Auto, not Cool, Off or Fan only, and that the set point is a few degrees above the current room temperature. Replace the batteries if the screen is blank or dim. After a power outage, some thermostats come back on in a different mode or schedule, so check that too.

Next, look at the air filter at the indoor air handler or return grille. A filter packed with dust starves the system of airflow, and a heat pump with poor airflow can deliver weak, lukewarm air or shut itself down on a safety limit. Replace it with the size printed on the frame, with the airflow arrow pointing toward the unit.

Then check power. A heat pump has two parts: the outdoor unit and the indoor air handler or furnace. Each usually has its own breaker in the main panel, and the outdoor unit also has a disconnect box on the wall next to it. If a breaker has tripped, reset it once from a dry spot. If it trips again, leave it off and call. Repeated tripping points to an electrical or compressor fault, and our breaker guide explains why resetting again and again is risky.

Finally, give the system time. Many heat pumps and thermostats have built-in delays of a few minutes before the compressor restarts. Changing the setting over and over can keep resetting that timer and make it look as if nothing is happening.

In cold, damp weather, frost forms on the outdoor coil. To clear it, the heat pump briefly reverses itself and sends heat to the outdoor coil. During this defrost cycle the outdoor fan stops, you may hear a whoosh when the valve switches, and a cloud of steam can rise from the unit. Lennox says the whole process usually takes 5 to 15 minutes, and that defrosting even when it is in the 40s outside is not unusual.

While it defrosts, the air from your vents can feel cool for a few minutes, or the thermostat may show Aux heat while backup heat covers the gap. That is the system protecting itself, not a breakdown.

It becomes a problem when the defrost does not work. Lennox advises having repeated or very long defrost cycles checked by a professional. Other warning signs are ice that keeps building until the coil or the whole unit is encased, ice on the top of the unit or fan blades, a fan that does not restart, and grinding or banging from the outdoor unit.

Do not chip or pry ice off the coil with a shovel, screwdriver or ice pick. The thin aluminum fins and refrigerant tubing are easy to puncture, and a refrigerant leak turns a service call into a much larger repair. Do not pour boiling water on it either. If it is frozen solid, switch to Emergency Heat and call.

Many homeowners in Indiana County and Westmoreland County grew up with gas or oil furnaces that blow very hot air. A heat pump moves heat from outdoor air into the house and delivers it at a lower temperature over longer run times. Air that feels lukewarm on your hand is normal if the house is holding the temperature you set.

Cold weather makes the gap bigger. EPRI notes that an air-source heat pump's heating capacity and efficiency fall as the outdoor temperature drops, which is why most systems are installed with backup heat, usually electric heat strips or, in a dual-fuel setup, a gas, oil or propane furnace. The U.S. Department of Energy says newer cold-climate heat pumps can keep heating in much colder regions, but an older standard model in a drafty house may simply run nonstop on the coldest nights.

The real test is the trend. If the house keeps dropping several degrees below the set point and does not recover even in milder weather, if the system runs on backup heat all the time, or if the air from the vents is cold for long stretches outside a defrost cycle, something is wrong. Low refrigerant from a leak, a failed reversing valve, a bad defrost control, a failed compressor or capacitor, or backup heat that is not working are common findings, and all of them need a technician with gauges and meters.

Aux or Auxiliary heat turns on automatically. The thermostat adds backup heat during defrost, on very cold days, and when you raise the temperature by several degrees at once. Seeing Aux for short periods is normal. You do not need to do anything.

Emergency Heat, often labeled EM or EMER, is a manual setting. Lennox explains that it shuts off the heat pump completely and runs only the backup source. Use it when the outdoor unit has clearly failed, is frozen solid or damaged by ice or storm debris, or when a technician tells you to. Electric heat strips use a lot more electricity than the heat pump, so expect a higher bill while it is on and switch back to normal Heat after the repair.

If the thermostat is showing EM and nobody knows why, set it back to Heat and watch whether the outdoor unit starts. If Emergency Heat does not warm the house either, the backup heat or the indoor unit may have a problem too, and the call is more urgent.

Large setbacks can also bring on backup heat. Turning the thermostat down to 60 at night and back up to 70 in the morning can make many thermostats run the heat strips to catch up. Smaller, steady changes are usually easier on the bill.

Losing heat in a Western Pennsylvania cold snap can quickly become a frozen pipe problem, especially in older homes in Indiana, Blairsville, Homer City, Greensburg, Latrobe, Jeannette and Murrysville with plumbing along outside walls or in crawl spaces. Open sink cabinet doors on outside walls, keep interior doors open, and let a faucet on an outside wall drip slightly.

Use only electric space heaters made for indoor use, plug them directly into a wall outlet, and keep them three feet from anything that can burn. Never heat the house with a gas oven, grill, camp stove or a generator. Generators belong outdoors, far from windows, doors and vents.

If you have a dual-fuel system with a gas, oil or propane furnace as backup, working carbon monoxide alarms matter. If a CO alarm sounds, get everyone outside and call 911 first. Keep snow cleared from around the outdoor unit and from any furnace vent pipes on the side of the house after a storm.