Heat pump not heating?
Before you call for service, run through these common causes — several are quick DIY fixes, and knowing the rest helps you avoid an unnecessary bill.
Quick checks first
- Thermostat set to "Heat" and above room temperature? Try "Emergency Heat" temporarily to test.
- Air filter clean? A clogged filter chokes airflow and cuts heat.
- Outdoor unit clear of snow, ice and debris?
Common causes it is not heating
| Symptom | Likely cause |
|---|---|
| Blowing cool air briefly | Normal defrost cycle (lasts a few minutes) |
| Outdoor unit iced over | Defrost control or sensor fault, or low refrigerant |
| Runs but weak heat | Dirty filter/coil, low refrigerant, or below the balance point |
| No power / not starting | Tripped breaker, capacitor or contactor failure |
| Only aux/strip heat runs | Compressor or reversing valve issue |
When to call a professional
Refrigerant, compressor, reversing-valve and electrical-component issues need a licensed HVAC tech. If basic checks do not restore heat — or the unit trips the breaker — book service. In deep cold, also confirm you are not simply below the unit's balance point, where backup heat should engage.
Frequently asked questions
Why is my heat pump blowing cold air?
Most often it is in a normal defrost cycle (a few minutes). Persistent cold air can mean a dirty filter, low refrigerant, a reversing-valve fault, or operation below the balance point.
Why is my heat pump frozen / iced over?
Light frost that clears during defrost is normal. Heavy, persistent ice points to a defrost-control fault, low refrigerant or restricted airflow — call a technician.
Should I use emergency heat?
Only as a temporary backup — it uses expensive resistance heat. If you rely on it, your heat pump likely needs service.
Related
Sources & further reading
Educational guide, reviewed against US DOE & ENERGY STAR guidance and updated June 2026. Estimates only — not a substitute for a professional assessment or Manual J load calculation.