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A heat pump not heating is often caused by a thermostat setting, a dirty filter, ice on the outdoor unit or a tripped breaker. More serious causes include low refrigerant or a failed reversing valve. Start with the simple checks below, then call our Worcester heat pump service if the house stays cold.
Key Takeaways
- Check the thermostat first. It must be set to HEAT with the fan on AUTO.
- Short bursts of cool air during defrost mode are normal in cold weather.
- Ice that never clears points to a defrost or refrigerant problem.
- A dirty filter or blocked outdoor unit is one of the most common causes.
- Refrigerant and reversing valve repairs require a licensed technician.
How a Heat Pump Heats Your Home
A heat pump does not burn fuel. It moves heat. In winter, the outdoor coil pulls heat from the outside air, even when it feels cold, and refrigerant carries that heat inside. A reversing valve switches the direction for summer cooling.
Because it moves heat instead of making it, a heat pump is very efficient. Massachusetts reports that an air-source heat pump can cut heating electricity use by up to 75%, according to a state heat pump announcement, compared to electric resistance heat such as baseboards. Since November 2025, the state’s major utilities also offer a seasonal reduced electric rate for eligible heat pump households. That efficiency depends on the system working correctly, so small problems matter.
Is a Heat Pump Blowing Cold Air Normal?
Sometimes. In cold, damp weather, frost forms on the outdoor coil. The heat pump switches to defrost mode for a few minutes to melt it. During defrost, you may feel cooler air and see steam from the outdoor unit. That is normal.
Air that feels lukewarm is also normal for many heat pumps. Supply air is often around 90 to 100 degrees, which feels cooler than furnace air even when the system is working. A heat pump blowing cold air for long periods is not normal.
8 Common Causes of a Heat Pump Not Heating
| Cause | What you may notice | DIY check? |
|---|---|---|
| — | — | — |
| Thermostat set wrong | No heating call, fan runs | Yes |
| Dirty air filter | Weak airflow, long run times | Yes |
| Tripped breaker | Indoor fan works, outdoor unit silent | Yes |
| Snow, ice or debris on outdoor unit | Coil blocked, unit struggles | Yes, gently |
| Defrost control failure | Ice builds and never clears | No |
| Low refrigerant | Lukewarm air, ice on coil, hissing | No |
| Reversing valve failure | Cools fine but will not heat | No |
| Failed backup heat | House falls behind on very cold days | No |
1. Thermostat Settings
Make sure the thermostat is on HEAT, not COOL or AUTO changeover set wrong. Set the fan to AUTO. If the display shows “EM HEAT” or “AUX,” read our guide on the EM heat setting explained so you know what each mode does.
2. Dirty Air Filter
A clogged filter restricts airflow over the indoor coil. The system runs longer, heats less and can trip safety controls. The EPA heat pump guidance recommends cleaning or changing filters monthly or as needed.
3. Tripped Breaker
Heat pumps usually have separate breakers for the indoor air handler and the outdoor unit. If one trips, part of the system stops. Reset it once. If it trips again, call a technician.
4. Blocked Outdoor Unit
Snow drifts, ice from a roof edge, leaves and bushes can block airflow at the outdoor coil. Keep about 2 feet of clearance around the unit. Clear snow gently by hand. Never chip ice off the coil with a tool.
5. Defrost Problems
If the outdoor coil stays covered in ice for hours, the defrost board, sensor or valve may have failed. The heat pump cannot pull heat through a solid block of ice.
6. Low Refrigerant
Refrigerant does not get used up. If it is low, there is a leak. Signs include lukewarm air, ice on the coil and hissing sounds. This is a job for a certified technician.
7. Reversing Valve Failure
If your heat pump cooled well last summer but will not heat now, the reversing valve may be stuck. This also needs a professional repair.
8. Backup Heat Not Working
Many heat pumps use electric heat strips or a furnace as backup on the coldest days. If backup heat fails, the house can fall behind during a deep freeze even if the heat pump itself is fine.
What to Check Before You Call
- Set the thermostat to HEAT, the fan to AUTO, and the temperature a few degrees above the room.
- Replace the thermostat batteries if the display is dim.
- Check and replace the air filter.
- Check both breakers for the indoor and outdoor units.
- Look at the outdoor unit and gently clear snow, leaves or debris.
- Make sure indoor vents and return grilles are open.
- Wait 30 minutes and check the air again.
If the heat pump is still not heating, call (978) 828-0157 and we will send a technician.
Heat Pump Not Heating in Cold Massachusetts Weather
Older heat pumps lose capacity as temperatures drop. On a very cold night, the system may run nonstop and still fall a degree or two behind. Modern cold-climate models hold their output much better. Our article on cold winter heat pumps explains what to expect.
Frequent on and off cycling is a different problem. If your system starts and stops every few minutes, see our guide to heat pump short cycling.
If you are thinking about upgrading, Mass Save offers Mass Save heating rebates for qualifying systems.
How to Prevent Heat Pump Heating Problems
Most no-heat calls can be avoided with simple habits and a yearly check.
- Book a fall tune-up. A technician checks refrigerant pressure, defrost controls, electrical parts and airflow before the cold arrives.
- Keep the outdoor unit clear. After each storm, make sure snow is not piling against the coil or blocking the top fan.
- Watch the roof line. Dripping water from a gutter can freeze on the unit and trap it in ice.
- Avoid big thermostat setbacks. Large temperature drops can force backup heat to run when you turn the heat back up.
- Replace filters on schedule. Check monthly during the heating season.
In many Worcester County homes, the outdoor unit sits on a pad close to the ground. Raising it on a stand or wall bracket keeps it above drifting snow and helps the defrost water drain away.
Frequently Asked Questions
Why is my heat pump running but not heating?
The most common reasons are a wrong thermostat setting, a dirty filter, or the unit being in defrost mode. If it runs for a long time and the air stays cool, low refrigerant, a failed reversing valve or a defrost problem is likely. Those need a technician.
Should I use emergency heat if my heat pump is not heating?
Use emergency heat only as a short-term backup while you wait for a repair. It relies on electric resistance or a backup furnace, which costs much more to run. Call a technician rather than leaving it on for days.
At what temperature does a heat pump stop heating?
Standard heat pumps lose a lot of capacity below about 25 to 30 degrees. Cold-climate heat pumps can keep heating well below zero. Backup heat usually helps on the coldest days either way.
Is it normal for my heat pump to have ice on it?
Light frost is normal and should clear during defrost mode. Thick ice that covers the coil and stays for hours is not normal and needs service.
Get Warm Air Flowing Again
A heat pump not heating can often be fixed quickly once the cause is found. Our technicians check refrigerant, defrost controls, airflow and backup heat so you are not left in the cold. Call The Comfort Specialists at (978) 828-0157 or schedule heat pump repair. We serve Worcester and Central Massachusetts, Monday to Friday, 8 AM to 5 PM, with emergency HVAC service help when you need it.
