Heat Pump Outdoor Unit Frozen? Normal Frost vs a Real Problem
In winter, a thin layer of frost on the outdoor unit is normal. Heat pumps are built to collect some frost and melt it off on their own. A unit that is encased in solid ice, with the coil hidden and the fan blocked, is not normal. If it stays that way, efficiency drops, the system can’t deliver heat, and parts can be damaged.
Rule of thumb: light frost that clears within about an hour or two is normal. Thick ice that keeps building, or ice on the top of the unit, needs attention.
Why frost forms in the first place
In heating mode, the outdoor coil runs colder than the outside air so it can absorb heat. When the air is around 0–7°C and damp, which is a typical Lower Mainland winter day, moisture in the air freezes onto the cold coil. The unit then runs a defrost cycle to melt it. Lots of frost on wet, foggy days is expected. What matters is whether it clears.
Common causes of a heat pump icing up
| Cause | What you may notice | Who fixes it |
|---|---|---|
| Defrost not starting (sensor, board or reversing valve fault) | Ice keeps building; you never hear the defrost “whoosh” or see steam | Technician |
| Low refrigerant (leak) | Ice on part of the coil or the small copper line; weak heat indoors | Technician (leak search and repair) |
| Water dripping onto the unit | Ice on the top panel or one side; gutter or downspout above | Homeowner (fix the gutter), or relocate the unit |
| Unit sitting too low | Ice building up from the base; melt water can’t drain away | Technician (raise on stand or bracket) |
| Blocked airflow | Leaves, plants, snow or a cover around the unit | Homeowner (clear 60 cm around it) |
| Outdoor fan not running | Compressor hums but the fan doesn’t spin | Technician (motor or capacitor) |
| Dirty indoor filter | Weak airflow from the vents or heads | Homeowner (replace or clean the filter) |
What you can safely do
- Check the indoor filter. Replace or clean it if it’s dirty.
- Clear around the unit. Remove leaves, snow and anything within about 60 cm. Remove any cover. Covers are for long-term storage, not for winter use.
- Look up. If a gutter or downspout drips onto the unit, fix that first.
- Let it defrost. Watch for 30–90 minutes. A healthy unit will stop, sometimes make a whoosh sound, release steam and drip water.
- If it is completely iced over, switch the thermostat to emergency/auxiliary heat (if you have it) or off, and call us. You can rinse the ice with lukewarm water from a garden hose.
When to call a technician
- Ice is back within a day after you cleared it
- The coil is fully covered and the fan blades are touching ice
- You see ice on the refrigerant lines going into the house
- The house is not warming up, or the system is blowing cold air
- The unit never seems to go into defrost
We diagnose the defrost controls, sensors, fan and refrigerant charge and fix the cause, not just the ice. Heat pump repair · Burnaby · Vancouver
Preventing ice build-up
- Book a yearly heat pump service that includes checking the defrost cycle and refrigerant charge
- Keep the unit raised on a stand or wall bracket so melt water can drain
- Keep gutters clear above the unit
- Change filters on schedule
Heat pump iced over right now?
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