Heat Pump Not Heating? Causes, Safe Checks & When to Call for Repair

If your heat pump is running but the house is not getting warm, or the system will not start heating at all, several different problems can produce the same symptom. Some are simple thermostat or airflow issues. Others involve defrost, backup heat, electrical controls, the outdoor unit, or the refrigeration system.

This guide focuses on low-risk checks a homeowner can make before requesting service. It does not recommend opening equipment panels, bypassing controls, handling refrigerant, or performing internal electrical repairs.

Start With the Thermostat

• Set the thermostat to HEAT, not COOL or AUTO.
• Set the target temperature a few degrees above the current room temperature.
• Check whether the thermostat display is blank or showing an error code.
• If your thermostat uses replaceable batteries, check them according to the thermostat manual.
• Do not make repeated large temperature jumps while troubleshooting.

Heat pumps often work best with a relatively steady thermostat setting. Some systems may bring on auxiliary heat when recovering from a large setback.

Check the Air Filter and Indoor Airflow

A dirty filter or restricted airflow can reduce heat transfer and make the system run longer while delivering less useful heat to the rooms.

• Inspect the accessible air filter and clean or replace it according to the equipment/filter instructions.
• Make sure supply registers are open and not blocked by furniture or rugs.
• Make sure return grilles are not blocked.
• Pay attention to whether airflow at the vents is unusually weak compared with normal operation.

Is the Heat Pump Blowing Cool or Lukewarm Air?

Heat-pump supply air can feel cooler than furnace air because a heat pump often delivers moderate-temperature air for longer periods. If the home is still reaching the thermostat setpoint, the system may be operating normally.

If the supply air feels cool and the indoor temperature keeps falling, that is different. The cause can involve controls, outdoor-unit performance, airflow, defrost, backup heat, or the refrigeration system.

See the Heat Pump Blowing Cold Air guide →

Check the Outdoor Unit

Look at the outdoor unit from a safe distance. Do not open the cabinet or reach into moving equipment.

• Is the outdoor unit running?
• Is it buried in drifting snow or surrounded by leaves or debris?
• Is there a light frost or a heavy layer of ice?
• Is there a new grinding, screeching, banging, or repeated buzzing sound?
• Is there active sparking, smoke, or a burning odor?

ENERGY STAR recommends keeping outdoor heat-pump equipment clear of snow, leaves, and other debris so airflow is not obstructed.

Light Frost vs. Heavy Ice

Some frost can be normal during heating operation in cold, damp weather. Heat pumps periodically enter a defrost cycle to melt frost from the outdoor coil. You may notice a temporary change in sound, steam around the outdoor unit, or a short change in indoor air temperature during defrost.

Heavy ice that does not clear, an outdoor unit encased in ice, or repeated loss of heating during defrost should be inspected. Do not chip ice from the coil or pour hot water over the equipment.

See the Frozen Heat Pump & Defrost guide →

What Does AUX Heat Mean When the Heat Pump Is Not Keeping Up?

Auxiliary heat is backup heat that supplements the heat pump when additional heating is needed. It may appear during very cold weather, during recovery from a large thermostat increase, or during some defrost conditions.

If AUX runs nearly all the time, the home still cannot maintain temperature, or backup heat does not seem to work, the system deserves professional diagnosis. For a deeper explanation, see Auxiliary Heat vs. Emergency Heat once that guide is published.

Why a Heat Pump May Stop Heating

• Thermostat or control problem: the system may not be receiving the correct call for heat.
• Dirty filter or airflow restriction: poor airflow can reduce performance and contribute to equipment problems.
• Defrost problem: the outdoor coil may remain heavily iced if the system cannot enter or complete defrost normally.
• Outdoor fan or motor problem: the outdoor unit may not be moving enough air.
• Electrical fault: controls, contactors, capacitors, wiring, breakers, disconnects, or other electrical components can fail.
• Refrigeration-system problem: refrigerant leaks, compressor problems, valves, or other refrigeration faults require professional diagnosis.
• Backup heat problem: electric resistance heat or dual-fuel backup may not operate when expected.
• System capacity/load mismatch: the heat pump may not be able to carry the building load under current conditions, particularly if sizing or building conditions are poor.

Heat Pump Runs Constantly but the House Is Still Cold

Long run times are not automatically a fault. Variable-capacity heat pumps can run for extended periods at lower output. The concern is when the system runs continuously while indoor temperature keeps moving away from the thermostat setpoint.

Check the filter, registers, thermostat mode, and outdoor-unit clearance. If the home continues losing temperature, request service.

Heat Pump Is Not Heating but the Indoor Fan Runs

If the indoor blower runs but useful heat is not being produced, the system may have a control problem, an outdoor-unit problem, a defrost issue, backup-heat problem, or refrigeration-system fault. A technician will need to determine which part of the heating sequence is failing.

What If the Breaker Tripped?

A breaker trip can indicate an electrical or equipment fault. Do not repeatedly reset a breaker that keeps tripping, and do not remove electrical panels or bypass a disconnect. Request HVAC or electrical diagnosis.

When No Heat Becomes Urgent

Loss of heat during severe winter weather can become a household safety issue even when the HVAC fault itself is not an electrical or fire emergency. Arrange service promptly if indoor temperatures are falling significantly.

If there is smoke, active sparking, fire, a strong burning smell, a gas odor, or a carbon monoxide alarm, stop ordinary troubleshooting and treat the situation as a safety emergency.

Heat Pump Not Heating FAQs

Why is my heat pump running but not heating?

Possible causes include incorrect thermostat settings, restricted airflow, defrost problems, backup-heat issues, outdoor-unit faults, electrical problems, or refrigeration-system problems. Start with the thermostat, filter, airflow, and outdoor-unit condition before requesting service.

Why is my heat pump blowing cold air?

Heat-pump air can feel cooler than furnace air while still warming the home. If the house reaches the thermostat setpoint, that may be normal. If room temperature keeps falling, have the system checked.

Why is my heat pump not heating after a snowstorm?

Check whether drifting snow or ice is blocking airflow around the outdoor unit. Remove only loose snow and debris that can be cleared safely. Do not chip ice from the coil. Persistent heavy icing needs service.

Should I switch to Emergency Heat if the heat pump is not heating?

Emergency Heat is system-specific. On many thermostats it is a manual backup-only mode. Check the thermostat/equipment instructions or professional guidance before changing modes.

Can a dirty filter make a heat pump stop heating properly?

A heavily loaded filter can restrict airflow and reduce system performance. ENERGY STAR recommends cleaning or replacing filters according to equipment guidance and when they are visibly dirty.

Sources

• ENERGY STAR: Air-Source Heat Pumps
• ENERGY STAR: HVAC Maintenance Checklist
• U.S. DOE Building Science Education: Air-Source Heat Pump FAQ

Request Heat Pump Repair in Eldora, IA

If the thermostat is calling for heat but the home is not warming, send the thermostat status, outdoor temperature, whether the outdoor unit is running, whether AUX heat is showing, and any ice, noise, odor, breaker, or error-code information with your service request.