If a heat pump is running but the home is not warming up, the cause may be as simple as a thermostat or airflow problem—or it may require professional diagnosis. This guide focuses on safe homeowner checks and the clues that help distinguish normal cold-weather behavior from a real heating fault.
Heat Pump Not Heating: Start With These Safe Checks
- Confirm the thermostat is in Heat mode and the setpoint is above room temperature.
- Check whether the thermostat or indoor unit has lost power.
- Inspect the air filter and obvious supply/return airflow blockages.
- Check whether the outdoor unit is buried in snow or blocked by debris.
- Look for a tripped breaker, but do not repeatedly reset one that trips again.
- Note whether auxiliary or emergency heat is running.
- Do not open electrical or refrigerant compartments.
Heat Pump Runs but No Heat Reaches the House
A heat pump can run for long periods in cold weather, so runtime alone does not prove there is a fault. What matters is whether indoor temperature is stable or rising, whether airflow is normal, whether the outdoor unit is operating, and whether backup heat is behaving as designed.
Heat Pump Blowing Cool or Lukewarm Air
Heat-pump supply air often feels cooler than furnace air. That can be normal. If the thermostat setpoint is being maintained, lower supply-air temperature does not automatically mean the system is failing. If the home continues to lose temperature, the system needs a closer look.
Heat Pump Not Heating in Cold Weather
As outdoor temperature falls, heat-pump capacity can change. A system that works well in milder weather may struggle if its low-temperature output is below the home’s heating load. The right comparison is between the home’s design load and the equipment’s manufacturer-rated capacity at the relevant outdoor temperature.
See heat pumps in cold weather, cold-climate heat pumps, and heat-pump sizing.
Outdoor Unit Is Frozen or Covered in Ice
Light frost can be normal, and heat pumps periodically enter defrost. Heavy ice that persists, blocks airflow, or quickly returns can point to a defrost, sensor, airflow, drainage, refrigerant, or installation problem.
Auxiliary Heat Is Running Constantly
Auxiliary heat can be normal during cold conditions or recovery from a thermostat setback. Constant or unexpected use can also indicate that the heat pump is not meeting the load, a control setting is forcing backup heat, or the primary system is underperforming.
Emergency Heat Is Not Working
Emergency heat is a backup mode, not a repair. If the primary heat pump is unavailable and the backup source also is not providing heat, the system needs professional diagnosis. Repeated breaker trips, burning smells, or abnormal electrical behavior should not be treated as DIY troubleshooting.
When to Request Heat Pump Repair
- The home keeps losing temperature.
- The system will not start.
- A breaker repeatedly trips.
- The outdoor unit remains heavily iced after normal defrost should have cleared it.
- There is a burning smell, unusual electrical behavior, or a new loud mechanical noise.
- Backup heat is unavailable or operating abnormally.
- The same heating problem keeps returning.
For local service information, see heat-pump repair & service.
Repair or Replace?
A no-heat event does not automatically mean the heat pump needs replacement. Diagnosis should come first. Replacement becomes a broader comparison when failures recur, a major component has failed, the system no longer meets the heating load, or the existing design itself is part of the problem.
Use the repair vs. replace guide and replacement page.
Heat Pump Not Heating FAQs
Why is my heat pump running but not heating?
Possible causes include thermostat/control issues, airflow problems, low outdoor capacity, defrost problems, backup-heat issues, electrical faults, or refrigerant-side problems. The symptom alone is not enough to identify the cause.
Why is my heat pump not heating to the set temperature?
The system may be underperforming, undersized for current conditions, relying on backup heat, or affected by airflow/control problems. Compare indoor temperature trend and outdoor conditions before assuming the equipment has failed.
Should I switch to emergency heat?
Emergency heat is typically intended as a backup mode when the heat-pump side cannot operate. It should not be used as a substitute for diagnosing an unresolved heat-pump problem.