Heat pump problem guide
Heat Pump Not Heating? What It Usually Means
Heat pumps behave differently from furnaces, so some things that look like trouble are perfectly normal, while others need a technician.
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Quick answer
When a heat pump appears to stop heating, it may just be defrosting, or running on a mild setting that feels cooler than furnace heat. Genuine faults include the wrong thermostat mode, a clogged filter, heavy ice or debris on the outdoor unit, a stuck reversing valve, low refrigerant, or a faulty defrost board. Begin by looking at the thermostat mode and the outdoor unit.
What may be going on
Likely causes
A normal defrost cycle
Frost collects on the outdoor coil when winter air is cold and wet. The system briefly reverses to melt it, so you may feel cool air indoors for a few minutes and see steam rising from the outdoor unit. That is expected.
Thermostat mode or settings
A thermostat set to cool, auto with odd setpoints, or emergency heat by mistake can change how the system behaves. Heat pump thermostats also have their own wiring for auxiliary heat.
Heavy ice that won't clear
Light frost is normal, but a coil encased in thick ice for hours points to a defrost control, sensor or airflow problem.
Blocked outdoor unit or dirty filter
Leaves, snow drifts or yard debris around the outdoor unit, or a clogged indoor filter, cut airflow and heating output.
Reversing valve or refrigerant issues
A part called the reversing valve flips the heat pump from cooling to heating mode. When it gets stuck, or refrigerant runs low from a leak, the heat pump may blow cool air all the time.
Safe first checks
- Check that the thermostat mode reads heat, since auto or cool can confuse things, and that the setpoint sits above the indoor reading.
- Replace the indoor air filter if it looks gray or clogged.
- With the system off at the thermostat, gently clear leaves, snow or debris from around the outdoor unit.
- Check the breaker for both the indoor and outdoor units and reset a tripped one once.
- If you see steam from the outdoor unit and cool air for a few minutes, wait for the defrost cycle to finish.
What not to do
- Don't hack at ice with a scraper or screwdriver; coil fins bend and tubing punctures easily.
- Don't pour hot water on the unit or remove its panels.
- Don't rely on emergency heat as a long-term setting.
- Don't handle refrigerant lines or connections.
When to call
When to call a technician
Most heat pumps have auxiliary or emergency heat, usually electric heat strips or a furnace, that supplements the heat pump in very cold weather. Emergency heat on the thermostat runs that backup alone. It can keep the house warm while you wait for service, but it usually uses more energy, so it's a stopgap rather than a fix.
Call a technician if the outdoor unit stays solidly iced, the system blows cool air long after a defrost cycle should have ended, or the outdoor fan or compressor won't run. Those signs point to controls, the reversing valve or refrigerant, which need trained hands. Learn more about heat pump repair.
- Ice covers the outdoor coil and doesn't clear for hours.
- Air from the vents feels cool even when the system runs steadily.
- The outdoor unit is silent while the indoor blower runs in regular heat mode.
- An aux or emergency heat light stays on constantly.
- You hear grinding, screeching or loud buzzing from the outdoor unit.
What a technician may inspect
- Testing the defrost control and coil temperature sensor.
- Reversing valve operation in heating mode.
- Measuring refrigerant charge and looking for oily leak spots.
- Outdoor fan motor, capacitor and compressor operation.
- Auxiliary heat strips and thermostat wiring.
Keeping it from happening again
Keep a clear space around the outdoor unit, especially after winter storms and in fall when leaves pile up. Change the filter regularly and schedule a check before the heating season so defrost controls and refrigerant levels are confirmed. Winters here bring plenty of cold, damp days when frost forms, so a heat pump that defrosts reliably matters.
Where to go next
Related service and market pages
Steam is usually a sign the heat pump is defrosting. For a few minutes the outdoor coil is warmed on purpose, and melting frost turns to visible vapor in the cold air. The cycle normally lasts a few minutes. Thick ice that never clears is a different matter and worth a call.
Use it as a backup when the heat pump has clearly failed and the house needs warmth until help comes. Emergency heat runs the backup heat source alone and typically uses more energy. In normal operation the thermostat brings in auxiliary heat automatically when it's needed, so leave it on regular heat.
Not necessarily. Heat pumps send out milder air over longer run times, and that air can feel cool on a hand held to the register. If the house reaches its setpoint, the system is doing its job. If rooms stay chilly, consider heat pump repair.
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