Quick Answer
If your heat pump isn't heating, first check: thermostat settings (make sure it's on HEAT, not COOL), air filter (clogged filters cause shutdowns), and circuit breakers. A heat pump in defrost mode temporarily blows cool air—this is normal. In very cold weather (below 35°F), heat pumps produce air that feels lukewarm compared to a furnace—this is also normal. If none of these apply, you likely have a refrigerant issue, failed reversing valve, or defrost system problem that needs professional repair.
Heat pumps work differently than furnaces, which confuses many homeowners when something seems wrong. Before you call for service, understand that some "problems" are actually normal heat pump behavior—while others definitely need attention.
First: Is It Actually a Problem?
Heat pumps behave differently than furnaces. Let's rule out normal operation first:
Normal: Lukewarm Air in Cold Weather
Heat pump supply air typically reaches 90-100°F, while furnaces produce 120-140°F air. So heat pump air feels "lukewarm" compared to what you might be used to. As long as your home reaches the thermostat setting, this is normal.
Normal: Cool Air During Defrost Cycle
When temperatures drop below 40°F, ice can form on the outdoor unit. Your heat pump periodically runs a defrost cycle—temporarily switching to cooling mode to melt the ice. During this 5-15 minute cycle, indoor air feels cool. This is normal and should happen only a few times per hour in cold weather.
How to Tell If It's Defrost
1. Thermostat Issues
The most common "heat pump not heating" cause is thermostat settings:
Thermostat Checklist
- Is it set to HEAT (not COOL or AUTO)?
- Is the set temperature HIGHER than current room temp?
- Are the batteries fresh?
- Is "Emergency Heat" or "Aux Heat" turned off? (It should be off for normal operation)
Try setting the temperature 5 degrees above room temp and wait 5 minutes for the system to respond.
2. Dirty Air Filter
A clogged air filter restricts airflow, which can cause the heat pump to overheat and shut down—or just perform poorly. This is the easiest thing to check and fix.
Pull out your filter. If you can't see light through it, replace it. Then give the system 30 minutes to reset if it overheated.
3. Tripped Circuit Breakers
Heat pumps typically have two breakers—one for the indoor air handler and one for the outdoor unit. Both must be on. Check your electrical panel and reset any tripped breakers.
Breaker Trips Repeatedly?
4. Outdoor Unit Issues
Go outside and check your heat pump unit:
Outdoor Unit Check
- Is the unit running at all? (You should hear the compressor and see the fan spinning)
- Is the unit buried in snow, leaves, or debris?
- Is the unit covered in ice? (A light frost is normal; a solid ice block is not)
- Is the disconnect switch near the unit in the ON position?
Clear any debris blocking airflow. If the unit is completely iced over and not defrosting, call for service.
5. Refrigerant Issues
Low refrigerant from a leak severely reduces heating capacity. Signs include:
- Heat pump runs constantly but home never reaches temperature
- Ice forming on the outdoor unit that won't defrost
- Hissing sounds near the unit
- Higher than normal electric bills
Refrigerant issues require professional diagnosis and repair. The leak must be found and fixed before recharging.
6. Failed Reversing Valve
The reversing valve switches your heat pump between heating and cooling modes. If it fails or gets stuck, your heat pump may only cool—blowing cold air when it should be heating.
Signs of a reversing valve problem: AC works fine in summer, but the system only blows cold air in winter even when set to heat. This requires professional repair.
7. Defrost System Problems
If your outdoor unit stays covered in ice and never defrosts, the defrost control board, defrost sensor, or related components may have failed. This causes the heat pump to run inefficiently and eventually stop heating altogether.
| Symptom | Likely Cause | DIY or Pro? |
|---|---|---|
| Lukewarm air (home still heats) | Normal heat pump operation | No action needed |
| Cool air for 5-15 min, then warm | Normal defrost cycle | No action needed |
| Cool air constantly | Reversing valve, refrigerant, or control issue | Call for service |
| Unit completely iced over | Defrost system failure | Call for service |
| Outdoor unit not running | Power issue, capacitor, or compressor | Check breaker, then call |
| Runs but home never warms | Refrigerant leak or sizing issue | Call for service |
When to Use Emergency Heat
Most heat pump systems have "Emergency Heat" or "Aux Heat" backup—usually electric resistance heating. This should only be used when:
- Your heat pump has completely failed and you need heat until it's repaired
- A technician advises using it temporarily
- Outdoor temperatures are extremely low (below 25°F for extended periods)
Emergency Heat = High Electric Bills
Heat Pump Repair Costs
Common Heat Pump Repairs
| Service | Cost | Notes |
|---|---|---|
| Capacitor replacement | $150-$300 | Common wear item |
| Refrigerant recharge + leak repair | $300-$1,000 | Depends on leak location |
| Reversing valve replacement | $500-$1,200 | Major repair |
| Defrost control board | $200-$500 | Common failure point |
| Compressor replacement | $1,500-$2,500 | Consider system age |
If you're in <a href="/services/heat-pump-repair/indian-trail">Indian Trail</a>, <a href="/services/heat-pump-repair/monroe">Monroe</a>, <a href="/services/heat-pump-repair/matthews">Matthews</a>, or surrounding Charlotte areas, we offer same-day heat pump diagnosis and repair. Our $89 diagnostic fee is waived with repair.
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Written by
Kodiak HVAC Team
HVAC professional at Kodiak Heating & Cooling.