Heat Pump Not Heating or Blowing Cold Air? What to Check First
It runs in winter, but the house stays cold or the vents blow cool air.
By Mark Curant·Updated
Most likely causes
- Thermostat on Cool or Auto, or a schedule holding a low temperature
- A defrost cycle in progress (cool air for a few minutes is normal)
- A clogged air filter
- The outdoor unit iced over or blocked by snow
- Backup (auxiliary) heat not working on the coldest days
- A reversing valve stuck in cooling mode, or low refrigerant
Before you open anything
Turn the system off at the thermostat, then switch off power at the breaker and at the disconnect beside the outdoor unit. Never touch the capacitor, even with the power off: it can hold a dangerous charge. Refrigerant work is for licensed technicians only. Reset a tripped breaker once; if it trips again, leave it off.
Heat strips run on a separate high-voltage circuit; don't open the air handler to check them. Never add refrigerant yourself: it requires EPA certification, and newer systems use mildly flammable refrigerants.
Check these first (free, 5 minutes)
- Thermostat: mode on Heat, set at least 2–3°F above the room, schedule or "hold" off. A heat pump thermostat may show "Aux" or "Em Heat"; leave Emergency Heat off for now.
- Feel the air at a vent after 10 minutes of running. Heat pump air feels lukewarm compared with a gas furnace; that's normal as long as the house slowly warms.
- Outdoor unit: is the fan spinning and is it free of thick ice and snow? A short burst of steam with the fan stopped is a normal defrost.
- Air filter: replace it if it's gray. Low airflow cuts heating just as it cuts cooling.
- Breakers: there are usually separate breakers for the outdoor unit, the indoor air handler and the backup heat strips.
Causes, signs and repair costs
Thermostat settings or schedule
DIYMode on Cool or Auto with a low setpoint, a schedule or vacation hold
Typical cost: $0
Normal defrost cycle
DIYCool air for a few minutes, outdoor fan stopped, steam rising from the unit, then heat resumes
Typical cost: $0 (normal)
See: Heat pump steaming / defrost →Clogged filter
DIYWeak airflow from vents, filter visibly gray
Typical cost: $5–$20
Outdoor coil iced over or buried in snow
DIY or proCoil encased in ice that doesn't clear, or snow drifted against the unit
Typical cost: $0 to clear snow; depends on the cause
See: Heat pump iced up →Outdoor unit not running
DIY or proIndoor fan runs, outdoor unit silent or humming; breaker off
Typical cost: $0 (breaker) to $150–$400 (capacitor)
See: Outdoor unit not running →Backup heat not working
ProHouse falls behind only on the coldest days; "Aux" shows but the air stays lukewarm; heat-strip breaker tripped
Typical cost: $75–$200 service call plus parts
Reversing valve stuck in cooling
ProAir from the vents is cold, not just lukewarm, all the time in Heat mode; the outdoor unit blows warm air
Typical cost: $350–$1,200
Low refrigerant (a leak)
ProHeating has gotten weaker over weeks, frequent icing, hissing or oily spots on the lines
Typical cost: $400–$2,400 to find, fix and recharge
| Cause | Signs | Who fixes it | Typical cost |
|---|---|---|---|
| Thermostat settings or schedule | Mode on Cool or Auto with a low setpoint, a schedule or vacation hold | DIY | $0 |
| Normal defrost cycleSee: Heat pump steaming / defrost → | Cool air for a few minutes, outdoor fan stopped, steam rising from the unit, then heat resumes | DIY | $0 (normal) |
| Clogged filter | Weak airflow from vents, filter visibly gray | DIY | $5–$20 |
| Outdoor coil iced over or buried in snowSee: Heat pump iced up → | Coil encased in ice that doesn't clear, or snow drifted against the unit | DIY or pro | $0 to clear snow; depends on the cause |
| Outdoor unit not runningSee: Outdoor unit not running → | Indoor fan runs, outdoor unit silent or humming; breaker off | DIY or pro | $0 (breaker) to $150–$400 (capacitor) |
| Backup heat not working | House falls behind only on the coldest days; "Aux" shows but the air stays lukewarm; heat-strip breaker tripped | Pro | $75–$200 service call plus parts |
| Reversing valve stuck in cooling | Air from the vents is cold, not just lukewarm, all the time in Heat mode; the outdoor unit blows warm air | Pro | $350–$1,200 |
| Low refrigerant (a leak) | Heating has gotten weaker over weeks, frequent icing, hissing or oily spots on the lines | Pro | $400–$2,400 to find, fix and recharge |
Typical U.S. installed prices in 2026. Most repairs also carry a service call fee of $75–$200, often credited toward the repair. See AC repair costs in 2026 for the full list.
Step by step
- 1
Set the thermostat correctly
Set it to Heat, 2–3°F above the room temperature, fan on Auto, and turn off any schedule or hold. If it was on Cool or Auto with a low setting, that alone explains cold air.
- 2
Rule out a defrost cycle
In cold, damp weather a heat pump reverses for a few minutes to melt frost off the outdoor coil. During defrost the outdoor fan usually stops, the unit may steam, and the indoor air can feel cool. If heat returns within about 15 minutes, nothing is wrong.
- 3
Replace the filter and open the vents
A clogged filter or closed vents cut airflow, which makes a heat pump run hotter and less efficiently and can trip its safety controls. Fit a new filter and make sure supply and return grilles are open and clear.
- 4
Clear the outdoor unit
Brush snow off the top and sides and keep 2 feet clear around it. If the coil is solidly encased in ice that a defrost doesn't clear, see the frozen outdoor unit page. Don't chip ice off the coil.
- 5
Use Emergency Heat only if the outdoor unit has failed
Emergency Heat turns the heat pump off and heats with the backup heat alone, usually electric strips that cost about two to three times as much to run. It's the right setting to stay warm while you wait for a technician, not an everyday setting.
Call a technician if
- The air is cold, not lukewarm, for more than 15 minutes in Heat mode
- The outdoor unit stays encased in ice after a defrost cycle
- The house can't keep up even on mild winter days
- A breaker for the outdoor unit or the heat strips trips again after one reset
Red flags on a quote
- A refrigerant top-up with no leak search: heat pumps don't use up refrigerant
- A reversing valve replacement quoted before anyone has checked the thermostat wiring and the valve's solenoid coil, which are cheaper fixes
- A new system quoted because "heat pumps don't work in the cold": cold-climate models are rated to heat well below freezing
Facing an expensive repair on an older system? Run it through the repair vs replace calculator, or read the $5,000 rule.
Is a heat pump worth it where you live?
Whether a heat pump saves money over a furnace depends on what you heat with now and what you pay for electricity. Our heat pump vs central AC guide runs the numbers for gas, propane, oil and electric baseboard heat.
See Heat pump vs central AC: what it costs to run.
Frequently asked questions
Why is my heat pump blowing cold air?
Most often it's in a defrost cycle, which lasts a few minutes and then heat returns. If the air stays cold, check that the thermostat is on Heat and set above the room temperature. Air that is cold all the time in Heat mode can mean the reversing valve is stuck in cooling, which needs a technician.
Is it normal for heat pump air to feel lukewarm?
Yes. A heat pump delivers a larger volume of moderately warm air rather than short blasts of hot air like a gas furnace, so the air at the vent can feel only lukewarm against your hand. As long as the house reaches the set temperature, it's working.
Should I switch my heat pump to Emergency Heat when it's very cold?
Usually not. The thermostat brings in backup (auxiliary) heat automatically when the heat pump needs help. Emergency Heat turns the heat pump off entirely, which costs much more to run. Use it only when the outdoor unit has failed or is iced solid and you're waiting for a repair.
At what temperature does a heat pump stop heating?
It depends on the model. Older and standard heat pumps lose a lot of capacity below about freezing and lean on backup heat, while cold-climate models are designed to keep heating at 5°F (−15°C) and below. Check the low-temperature rating on your model's spec sheet.
Related problems
Heat pump steaming / defrost
Steam from the outdoor unit, a whoosh, the fan stopping, cool air for a few minutes.
Heat pump iced up
Frost or thick ice on the outdoor unit that doesn't clear.
Outdoor unit not running
The indoor fan blows but the outside unit is silent, humming or its fan is still.
Fixed it? Check what it costs to run
If your system is old enough to keep breaking, compare its running cost with a new one before the next repair.
Open the SEER savings calculator