A heat pump that won’t heat is most commonly caused by a faulty reversing valve, low refrigerant charge, a failed capacitor, or a stuck defrost cycle. In most cases, a NATE-certified technician can diagnose and repair the issue within 1–3 hours.
Most Common Reasons a Heat Pump Won’t Heat
1. Faulty Reversing Valve
The reversing valve controls whether your heat pump operates in heating or cooling mode. When it sticks or fails, your system may only cool — or blow air that isn’t warm enough. This is one of the most common reasons a heat pump fails to heat in winter. Reversing valve repair costs $250–$600.
2. Low Refrigerant Charge
Heat pumps transfer heat using refrigerant. If there’s a leak or the refrigerant level has dropped, the system can’t efficiently extract heat from outside air. Signs include ice buildup on coils and longer run times with poor heating. A refrigerant recharge costs $150–$300 and requires an EPA 608 licensed technician.
3. Failed Capacitor
The capacitor starts and powers the compressor and fan motors. When it fails, the heat pump may hum, start briefly, or refuse to start altogether. Capacitor replacement is one of the fastest repairs — usually completed in under 1 hour for $90–$175.
4. Stuck Defrost Cycle
Heat pumps defrost themselves periodically in cold weather. If the defrost cycle gets stuck in defrost mode, the system blows cool air. If defrost is running constantly, there may be a sensor or control board issue.
5. Dirty Air Filter
A clogged air filter restricts airflow, causing the heat pump to work harder with less output. Replace your filter every 1–3 months. This is the one issue homeowners can fix without a technician.
6. Thermostat Set to Wrong Mode
Verify your thermostat is set to “Heat” (not “Cool” or “Fan Only”) and the temperature setpoint is above the current room temperature. This sounds obvious, but it accounts for a surprising number of service calls.
When to Call a Professional
If your heat pump is blowing cold or room-temperature air, making unusual noises, or has ice buildup on the outdoor unit, call a NATE-certified technician. Refrigerant work, reversing valve repair, and electrical diagnosis all require a licensed professional.
Why is my heat pump not heating?
The most common causes are a faulty reversing valve, low refrigerant charge, a failed capacitor, or a stuck defrost cycle. A NATE-certified technician should diagnose the exact cause.
Can a heat pump lose its ability to heat but still cool?
Yes. If your heat pump cools but won’t heat, the reversing valve is likely stuck in cooling mode. This is a common repair that restores both modes.
How much does it cost to fix a heat pump that won’t heat?
Repair cost depends on the cause: capacitor replacement ($90–$175), reversing valve repair ($250–$600), refrigerant recharge ($150–$300), or compressor repair ($600–$1,200).