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Heat Pump Not Heating?
What Bay Area Homeowners Should Check

Your heat pump cools fine but won’t switch to heating mode, or it blows cool air when set to heat. Heat pumps have unique failure modes that differ from traditional furnaces. Here’s what to check before calling for heat pump service.

Heat pump completely dead?

See AC/Heat Pump Won’t Turn On — same troubleshooting applies.

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Common Causes

Heat pumps reverse the refrigeration cycle to provide heat. When heating fails specifically, these are the usual reasons.

Stuck Reversing Valve

The reversing valve switches the heat pump between cooling and heating modes. When it sticks, the system stays in cooling mode even when set to heat. This is the #1 heat-pump-specific failure. You’ll feel cool air from the vents when heating is called for.

Thermostat in Wrong Mode

Heat pumps have specific thermostat settings. Make sure the system is set to HEAT (not COOL, not EMERGENCY HEAT unless needed). Some thermostats have a separate “Heat Pump” setting that must be configured correctly during installation.

Outdoor Unit Iced Over

In heating mode, the outdoor coil absorbs heat from outside air and can accumulate frost. The defrost cycle should handle this. If the defrost cycle fails, ice builds up until the unit can’t absorb heat. See our heat pump freezing guide.

Low Refrigerant

A heat pump needs proper refrigerant charge for both heating and cooling. Low refrigerant reduces heating capacity significantly. The system runs but the air is barely warm. Always indicates a leak that needs professional repair.

Auxiliary/Emergency Heat Not Engaging

Dual-fuel and hybrid systems use a backup heat source (electric strips or gas furnace) for very cold conditions. If the backup fails, you lose heating capacity when outdoor temps drop below ~35°F. Common in Bay Area hillside homes in Los Gatos and Saratoga.

Safe Checks You Can Perform

Verify thermostat settings. Set to HEAT, not COOL or AUTO. Temperature set above current room temp. Fan on AUTO. Try cycling the system off for 5 minutes then back on.

Check the outdoor unit. Is it running? Is it covered in ice? Light frost is normal in heating mode. Heavy ice buildup is not — see our freezing guide. Clear any debris or snow from around the unit.

Check the air filter. Replace if dirty. Restricted airflow affects heating performance just as much as cooling.

Try Emergency Heat. If your thermostat has an EM HEAT or AUX HEAT setting, switch to it temporarily. If you get warm air, the backup system works — the heat pump itself has the problem (likely reversing valve).

Check both breakers. Heat pump systems often have separate breakers for the outdoor unit and indoor air handler. Both must be on.

Signs You Need a Professional

System cools but won’t heat — stuck reversing valve. This is a professional repair — the valve needs to be replaced or the solenoid repaired.

Outdoor unit heavily iced over — defrost system failure. Needs professional diagnosis of the defrost timer, sensor, or control board.

Emergency heat works but normal heat doesn’t — confirms the heat pump outdoor unit has the issue (reversing valve, refrigerant, or compressor).

Neither heat pump nor emergency heat works — power issue, control board failure, or thermostat wiring problem. Needs full system diagnosis.

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Frequently Asked Questions

Why does my heat pump blow cool air in heating mode?

The most common cause is a stuck reversing valve — the component that switches between heating and cooling modes. Other causes include low refrigerant, thermostat misconfiguration, or a frozen outdoor unit. Try switching to Emergency Heat as a temporary solution while you schedule a repair.

Do heat pumps work in cold Bay Area weather?

Yes — modern heat pumps perform well down to about 5°F. Bay Area temperatures rarely drop below 30°F, making this region ideal for heat pump heating. For the handful of nights that dip into the low 30s, a dual-fuel system with gas backup handles it seamlessly. Read our heat pump vs furnace comparison.

How much does reversing valve replacement cost?

Reversing valve replacement typically runs $800–$2,000 including parts and labor, depending on the system. Sometimes the solenoid coil (which controls the valve) is the only failed component — that’s a much cheaper repair at $200–$400. We diagnose which component has failed before recommending replacement.

Heat Pump Not Heating?

Same-day heat pump diagnosis and repair. We service all brands including Mitsubishi, Daikin, Carrier, and more.