Heat Pump Iced Over? When It’s Normal and When to Call
Frost or steam on a heat pump’s outdoor unit usually means it’s defrosting, and the ice clears on its own within minutes. A unit that stays iced, blows cold air for an hour, or wears a glaze of freezing rain needs a different response. Here’s how to tell them apart, and when to call Borum Heating & Air for heat pump repair in Amelia County, Powhatan and Cumberland.
Is it normal for a heat pump to ice over?
Yes. Light frost on a heat pump’s outdoor coil is normal on cold, damp days, and the system clears it with a built-in defrost cycle. In heating mode the outdoor coil runs colder than the outside air, so moisture freezes on it. As often as every 30 to 90 minutes, the heat pump reverses itself for a few minutes (usually 3 to 5) to warm the coil and melt the frost. During defrost the outdoor fan stops, you may hear a whoosh, and a cloud of steam rises off the unit. Then it switches back to heating. Your thermostat may show “AUX” while this happens, because backup heat keeps the house warm in the meantime.
Why is my heat pump blowing cold air?
A heat pump blowing cool air is often working normally. Heat pump air usually leaves the vents at about 90 to 110 degrees, much cooler than a furnace’s, so it can feel lukewarm on your hand even while it heats the house. The air can also feel cooler for a few minutes during a defrost cycle. If the air stays cool after 30 to 60 minutes of steady running and the house keeps losing ground, something is wrong. Common causes are a defrost control that never ends the cycle, a stuck reversing valve, low refrigerant, or an outdoor fan or compressor that has stopped.
What’s the difference between aux heat and emergency heat?
Aux heat comes on by itself; emergency heat is a setting you choose. Both use the same backup source: usually electric heat strips in the indoor air handler, sometimes a gas or propane furnace. Aux heat helps the heat pump during defrost, on the coldest days, and when you raise the thermostat more than 3 or 4 degrees at once. Emergency heat shuts the heat pump off and runs the house on backup heat alone.
| Setting | Who turns it on | When to use it |
|---|---|---|
| Heat | You | Normal winter operation |
| Aux heat | The thermostat, automatically | Never set by hand |
| Emergency heat | You, manually | Outdoor unit failed or iced over |
Running on strips costs more. Heat strips turn each unit of electricity into one unit of heat, while a working heat pump moves more heat into the house than the electricity it uses.
What should I do when freezing rain coats my heat pump?
Freezing rain is not frost, and the defrost cycle can’t clear it. Defrost only warms the coil from the inside. A glaze of ice on the fan blades, the fan grille or the top of the cabinet stays put, and an iced fan blade strains the motor every time it tries to turn. When ice coats the outside of the unit or the fan can’t spin, switch the thermostat to Emergency Heat. That rests the outdoor unit while the house stays warm, which is the guidance Lennox gives homeowners for a frozen heat pump. Once temperatures rise above freezing, the ice usually melts in 2 to 4 hours. Then switch back to Heat.
Two things not to do: don’t chip at the ice, which bends fins and damages the coil, and don’t pour hot water on the unit, since the sudden temperature change can crack parts. If the ice hasn’t cleared within 6 to 8 hours of thawing weather, or it refreezes as soon as the unit runs, call for service.
What can I safely check before calling?
These take five minutes and sometimes save a service call:
- Thermostat. Set it to Heat, fan on Auto, and a setpoint a few degrees above the room.
- Filter and returns. Replace a dirty filter and clear furniture off return grilles. Poor airflow makes the coil ice faster.
- Around the unit. Brush leaves or snow away from the sides and top by hand. Keep a couple of feet of clearance.
- Time. Give a possible defrost 15 minutes before deciding something is wrong.
- Breaker. Reset a tripped breaker once. If it trips again, leave it off and call.
When does an iced-over heat pump need a repair call?
Call Borum Heating & Air when any of these show up. They point to a repair, not a normal defrost:
- Ice covers the coil and never clears, or comes back right after a defrost
- The outdoor fan never runs in heating mode
- Grinding, screeching or banging from the outdoor unit
- A breaker that trips again after one reset
- Only cool air after 30 to 60 minutes of run time
- A burning or electrical smell: turn the system off and call
- A carbon monoxide alarm: get everyone outside and call 911 first. A heat pump burns no fuel, but a gas or propane backup furnace does.
Ice that won’t clear usually traces back to a failed defrost sensor or control board, low refrigerant, or poor airflow. One customer wrote in January 2026 to thank our team for “fixing our heat pumps after hours knowing that it was going to dip down in the teens.” Book heat pump repair or call (804) 561-6001.
If your heat pump is 10 to 15 years old and icing up every winter, ask your technician whether repair still makes sense or whether it’s time to look at heat pump replacement.
How do you keep a heat pump from icing up?
Regular maintenance catches most causes of a heat pump that ices up. A heating tune-up checks the defrost sensor and controls, refrigerant charge, outdoor fan and airflow, which are the parts that fail when ice won’t clear. Borum’s Preventative Maintenance Agreement includes two visits a year, priority service, discounted diagnostic fees and no overtime charges. Our guide covers what a maintenance plan costs and when it’s worth it. Around the house, keep gutters and roof edges from dripping onto the outdoor unit, since that water refreezes on the cabinet and fan.
Frequently Asked Questions
Does Borum Heating & Air come out after hours for a frozen heat pump?
Yes. Borum Heating & Air offers 24-hour service, seven days a week, across Amelia County, Powhatan and Cumberland. Planned Maintenance Agreement members get priority service and no overtime charges. Call (804) 561-6001.
Will emergency heat damage my system?
No. Emergency heat is safe to run, but it costs more because the house heats on backup heat alone. Switch back to Heat once the outdoor unit is thawed or repaired, and call for service if you need emergency heat for more than a day.
Why does my thermostat say AUX?
AUX means backup heat is helping. That’s normal during a defrost cycle, on very cold days, and after a big jump in the thermostat setting. If AUX stays on for hours when it’s above 40 degrees outside, the heat pump may not be carrying its share and should be checked.
Get Your Heat Back On in Amelia County
If your heat pump is iced over and the house is getting cold, Borum Heating & Air can diagnose it, day or night. Call (804) 561-6001 or request service online.