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A heat pump not heating is most often caused by a wrong thermostat setting, a dirty filter, a normal defrost cycle or a frozen outdoor unit. Bigger causes include low refrigerant, a stuck reversing valve or a failed capacitor. Start with the simple checks below. If the house keeps getting colder, our Belmont heat pump repair team can find the cause fast.
Key Takeaways
- Check the thermostat first. Heat mode, fan on Auto, and set a few degrees above room temperature.
- Cool air for a few minutes in winter can be a normal defrost cycle, not a breakdown.
- Heavy ice that stays for hours on the outdoor unit means something is wrong.
- Refrigerant, valve and electrical problems need a licensed technician.
- Heat pump air feels cooler than furnace air, even when it works fine.
Why Is My Heat Pump Not Putting Out Heat?
When you find your heat pump not heating, the cause usually comes down to a setting, airflow or ice. The thermostat may be on Cool or the fan on On. A clogged filter can choke airflow. The outdoor coil may be in defrost or frozen solid. Less often, low refrigerant, a stuck reversing valve or a dead capacitor stops the heat.
Is It Broken or Just Working Differently?
A heat pump does not burn fuel. It moves heat from the outdoor air into your home. The ENERGY STAR heat pumps page notes that a heat pump can deliver up to three times more heat energy than the electricity it uses.
The trade-off is air temperature. Air from a heat pump vent often feels warm, not hot. Your body is about 98 degrees, so slightly warm air can feel cool on your skin. That alone is not a problem. A house that will not reach the set temperature is.
8 Reasons Your Heat Pump Is Not Heating
1. Thermostat Settings
It sounds simple, but it is one of the most common causes. Check that the thermostat says Heat, not Cool or Auto with a low setting. Set the fan to Auto. If the fan is set to On, it blows room air between heating cycles, which feels cold. If you see “Emergency” or “EM Heat” lit, read our guide to the emergency heat setting explained.
2. Dirty Air Filter
A clogged filter cuts airflow. The heat pump overheats inside, shuts off on a safety limit, and blows weak air. Swap the filter and see if heat returns.
3. Normal Defrost Cycle
In cold, damp weather, frost forms on the outdoor coil. The heat pump runs a defrost cycle to melt it. During defrost, you may see steam outside and feel cool air inside for several minutes. Then normal heat resumes. This is expected.
4. Frozen Outdoor Unit
A thin frost is normal. A thick block of ice that does not clear is not. It can mean a failed defrost sensor or board, low refrigerant, a stuck outdoor fan, or gutters dripping onto the unit.
5. Blocked Outdoor Unit
Leaves, pine straw, mulch and shrubs around the unit block airflow. Keep about two feet of open space on all sides.
6. Low Refrigerant
Refrigerant does not get “used up.” If it is low, there is a leak. Low charge leads to weak heat, ice, and long run times. A technician needs to find and fix the leak, then recharge the system.
7. Stuck Reversing Valve
The reversing valve switches the heat pump between heating and cooling. If it sticks in cooling, your system blows cool air in heat mode. A coil or valve repair fixes it.
8. Electrical Failure
A failed capacitor, contactor or control board can stop the outdoor compressor or fan. You may hear a hum or click outside with no fan movement. Thermostat wiring and low batteries can also cut the call for heat. Our post on common thermostat problems covers those.
Quick Symptom Guide
| What You Notice | Likely Cause | DIY or Call? |
|---|---|---|
| Cool air, fan running constantly | Fan set to On | DIY: set fan to Auto |
| Cool air for a few minutes, steam outside | Normal defrost | No action needed |
| Weak airflow from vents | Dirty filter or blocked return | DIY: change filter |
| Thick ice on outdoor unit for hours | Defrost failure, low refrigerant or fan issue | Call |
| Cool air in heat mode all the time | Reversing valve or refrigerant | Call |
| Outdoor unit hums but fan does not spin | Capacitor or motor | Call |
| Nothing runs at all | Breaker, thermostat or control problem | DIY check, then call |
Signs It Is Time to Call a Technician
- The house falls below the set temperature and keeps dropping.
- Ice covers the coil and does not clear after a defrost cycle.
- You hear grinding, buzzing or banging from the outdoor unit.
- The breaker trips again after one reset.
- Backup heat runs all the time, and your power bill jumps.
How to Troubleshoot a Heat Pump Safely
- Set the thermostat to Heat, fan to Auto, and three degrees above room temperature.
- Replace the thermostat batteries if the screen is dim or blank.
- Change the air filter.
- Check both breakers. Heat pumps usually have one for the indoor unit and one for the outdoor unit. Reset a tripped breaker once.
- Clear the outdoor unit of leaves and debris. Do not chip ice off the coil, since that can puncture it.
- Wait 30 minutes and check the vents again.
If you still have a heat pump not heating after these checks, call Gerald Griffin Heating and Cooling at (980) 277-5122. Our 24-hour emergency HVAC service covers cold nights, weekends and holidays.
How to Keep Your Heat Pump Heating All Winter
- Book a fall tune-up so refrigerant, defrost controls and electrical parts are checked before the cold.
- Keep the outdoor unit clear and make sure gutters do not drip on it.
- Change filters on schedule.
- Use small thermostat setbacks. Big setbacks can make a heat pump lean on costly backup heat. ENERGY STAR smart thermostats adjust settings for you automatically.
Heat Pump Not Heating FAQs
How do you reset your heat pump?
Turn the thermostat off. Switch off both heat pump breakers for about five minutes. Turn them back on, then set the thermostat to Heat. Some units also have a reset button on the outdoor unit or air handler. If it fails again soon after, call for service.
How long does it take for a heat pump to reset?
Many heat pumps have a built-in delay of about five minutes before the compressor restarts. This protects the compressor. Give it 10 to 15 minutes before judging the result.
What is auxiliary heat on a heat pump?
Auxiliary heat is the backup heat that helps the heat pump when it cannot keep up, often electric heat strips or a gas furnace. It turns on by itself. Emergency heat is the same backup, turned on manually.
Is a heat pump cheaper than gas?
It depends on local electric and gas rates and how cold it gets. In mild weather, a heat pump is often cheaper to run. In deep cold, gas can win, which is why some homes use a dual fuel system.
Can I install a heat pump myself?
No. Installing a heat pump means handling refrigerant, high-voltage wiring and sizing math. Refrigerant work requires EPA certification, and North Carolina requires a licensed heating contractor.
Get Your Heat Back Tonight
A heat pump not heating on a cold night is not something to guess about. Call Gerald Griffin Heating and Cooling at (980) 277-5122 and tell us what you see at the thermostat and the outdoor unit. A licensed technician will diagnose the problem and explain the fix before any work starts. We serve Belmont, Gastonia, Mount Holly, Cramerton, Dallas and nearby towns. You can also request heat pump service online.
Gerald Griffin Heating and Cooling Services
902 Belmont Mt Holly Rd
Belmont, NC 28012
Phone: (980) 277-5122
Hours: Open 24 hours
NC Heating Contractor License #32307