Heat pump trouble, one phone call
HVAC Rescue Pros is a call-connection service, not a contractor. Call (813) 471-5413 and you are connected with an independent local heating company that serves your ZIP code. The call costs you nothing, and the pro you speak with agrees pricing and scheduling with you directly.
How a heat pump heats your home
A heat pump doesn't burn fuel to make heat. It moves heat. Refrigerant picks up heat from the outdoor air, even cold air, and the compressor carries it indoors. In summer the same system runs in reverse to cool.
That explains a few things. Heat pump air feels warm, not hot, so it can seem lukewarm on your hand even when everything works. In cold weather it runs long cycles. And as it gets colder outside, backup heat helps out: usually electric heat strips in the indoor unit, or a gas furnace on dual-fuel systems.
Normal vs. not normal
| What you notice | Normal | Call a pro if |
|---|---|---|
| Steam rising from the outdoor unit | During defrost, for a few minutes, with a whoosh as it switches | It looks like smoke or smells like burning |
| Frost on the outdoor coil | A light white coat that melts during defrost | Solid ice covers the coil or the whole unit and doesn't clear within about an hour |
| Outdoor fan stops | Briefly during defrost | It stays still while the unit hums or runs |
| "AUX HEAT" on the thermostat | On very cold days, during defrost, or after a big jump in the setting | It shows all the time, even in mild weather |
| Long run times | On cold days, with the house holding temperature | It runs nonstop and the house keeps getting colder |
Heat pump symptoms at a glance
| Symptom | Common causes | What you can safely check |
|---|---|---|
| Cool air in heat mode | Wrong thermostat mode, stuck reversing valve, low refrigerant | Mode on HEAT, setting above room temperature |
| Outdoor unit iced solid | Defrost control or sensor, low refrigerant, outdoor fan, roof water dripping on it | Clear snow around it, check for gutter drips; don't chip ice |
| Indoor fan runs, outdoor unit doesn't | Tripped breaker, capacitor, contactor, thermostat wiring | Breaker for the outdoor unit, reset once |
| Runs nonstop, house stays cool | Low refrigerant, dirty filter, iced coil | Filter, vents open, outdoor unit clear |
| Hums or buzzes but won't start | Failed capacitor, worn contactor, compressor trouble | Turn it off at the thermostat and call |
| Nothing runs at all | Power, thermostat, blown fuse in the indoor unit | Thermostat display and batteries, breakers |
Common causes, explained
Reversing valve
This valve switches the refrigerant flow between heating and cooling. If it sticks or its coil fails, the system can blow cool air in heat mode. A technician confirms it with pressure and temperature readings.
Defrost control and sensor
A board and a sensor on the outdoor coil decide when to defrost. If either fails, frost builds into solid ice, airflow stops and heating drops off.
Refrigerant leak
The refrigerant circuit is sealed, so low refrigerant means a leak. Expect weak heat, icing and long run times. A pro should find and repair the leak, not just add refrigerant.
Outdoor fan motor
The fan pulls air across the outdoor coil. When it fails, the coil ices up quickly and the compressor can overheat and shut off.
Capacitor and contactor
The capacitor gives the motors their starting kick. The contactor is the switch that turns the outdoor unit on. Both wear out, and both are common repairs.
Thermostat wiring and settings
A heat pump thermostat tells the reversing valve which way to run. After a thermostat swap, one wrong setting or wire can mean cooling when you want heat.
What you can safely check
- Thermostat. Mode on HEAT (not COOL, and not EM HEAT unless on purpose), setting a few degrees above room temperature, fresh batteries.
- Air filter. Replace a dirty one. Ductless wall units have washable filters behind the front cover.
- Breakers. The indoor and outdoor units often have separate breakers. Reset a tripped one once. If it trips again, leave it off and call.
- Outdoor unit. Brush away snow, leaves and drifts so air can flow, and keep a couple of feet clear around it. Do not chip or pry at ice: the coil is thin and easy to puncture.
- Vents. Make sure supply and return vents are open and not blocked.
Emergency heat: when to use it, and why not for long
Emergency heat (EM HEAT) turns the heat pump off and runs only the backup heat. Aux heat is different: the thermostat adds backup heat automatically while the heat pump keeps working.
Switch to emergency heat when the outdoor unit is clearly in trouble: iced solid, grinding or banging, or not running at all. It keeps the house warm and protects the compressor until help arrives.
Don't leave it on for days. Electric heat strips use far more electricity than the heat pump, so your electric bill can climb fast, and they may not keep up on very cold nights. If your system has no backup heat, emergency heat does nothing. Use it as a bridge, then call.
Heat pump safety
While you wait, close curtains and doors. Give a space heater clear space, plug it into a wall outlet and never leave it unattended. To protect pipes in a cold house, let faucets drip, and check on older relatives, babies and anyone who is sick. The no-heat checklist and emergency heating repair pages have more. Gas furnace or boiler instead? See furnace repair or boiler repair.
