If your heat pump is not heating in cold weather, the most common cause on Vancouver Island is not a fault at all: it is the defrost cycle. On frosty, damp mornings the outdoor coil ices up, and the unit pauses heating for a few minutes to melt it. That is normal. A fault looks different: ice that never clears, no warm air for long stretches, or a blinking error code. Here is how to tell them apart and what you can safely check yourself.
Is it defrost mode? What normal looks like
When the outdoor temperature is near or below freezing, moisture in the air freezes on the outdoor coil. Natural Resources Canada explains that to clear it, the reversing valve switches the system into cooling mode, sending hot refrigerant gas to the outdoor coil while the outdoor fan shuts off. During that time the indoor side is not heating, and on a ducted system the air in the ducts is briefly cooled. Signs you are watching a normal defrost:
- The outdoor fan stops but the unit still hums.
- A cloud of steam rises from the outdoor unit. It is water vapour, not smoke.
- You hear a whoosh or click when it switches into and out of defrost.
- A ductless head stops blowing or slows to a crawl, often with its indicator light flashing; a ducted system blows cool air for a short time.
- Water drips or runs from under the outdoor unit afterwards.
Then heating resumes on its own. Victoria's damp coastal air near freezing is close to the worst case for frost, so frequent defrost cycles on a raw, foggy morning just above freezing are expected.
Defrost or fault? A quick comparison
| What you see | Probably normal if | Call for service if |
|---|---|---|
| Air from vents feels lukewarm | The room is still reaching its setpoint | The room temperature keeps dropping for an hour or more |
| Frost on the outdoor coil | A light, even layer that clears after each defrost | Thick ice that stays, or ice building up on the top or fan |
| Steam from the outdoor unit | It lasts a few minutes, then stops | You see smoke, smell burning, or the breaker trips |
| Indoor unit stops blowing | It restarts within several minutes | It stays off and shows a blinking error code |
| Cools in summer but will not heat | Not normal | Possible reversing valve or control fault |
| Short on and off cycles | Occasional, in mild weather | Constant, even on cold days |
Why does heat pump air feel cooler than a furnace?
Even when everything is working, many people coming from oil or gas think the heat pump is weak. Natural Resources Canada notes heat pumps heat a larger volume of air to about 25 to 45°C, while furnaces deliver less air at 55 to 60°C. Air below your skin temperature feels cool on your hand at the register, even though it is warming the room. Judge the system by the room thermostat, not the feel of the vent.
Heat pump not heating in a cold snap: what changes below freezing
Heat pumps move heat from outdoor air. As it gets colder there is less heat to move, so output and efficiency fall. In Victoria this rarely matters: the BC Building Code lists the city's January design temperature at -4°C. In an Arctic outflow cold snap, though, an older or undersized unit can run flat out and still lose ground. Natural Resources Canada adds that most air-source heat pumps have a minimum operating temperature, from -15°C to -25°C on newer models, below which a backup system must take over.
What provides backup depends on your system: baseboards left in place, electric strips in a ducted air handler, or a gas furnace in a dual fuel setup. If your backup has been disconnected and the heat pump is struggling on the coldest nights, that is a sizing or equipment question, not a repair. Our explainer on cold-climate heat pump ratings shows how to check a unit's capacity at low temperatures.
Safe checks you can do before calling
- Check the mode and setpoint. Make sure the thermostat or remote is on Heat (not Cool, Dry or Fan) and set above room temperature. Replace remote or thermostat batteries.
- Do not use deep setbacks. Natural Resources Canada recommends setbacks of no more than 2°C for heat pumps, because they recover slowly. Turning it down 5°C overnight can leave the house cold all morning.
- Check the filter. Clean or change it; NRCan suggests every 3 months. A clogged filter cuts airflow and can trigger safety shutdowns. On ductless heads, rinse the mesh screens.
- Clear around the outdoor unit. Brush off snow and leaves and keep a clear space around it. Make sure meltwater can drain away and is not refreezing under the unit.
- Do not chip or pry ice off the coil. The aluminium fins and refrigerant tubes are thin. Let the defrost cycle do it, or call for service if the ice will not clear.
- Check the breakers. If a breaker for the heat pump has tripped, reset it once. If it trips again, leave it off and call.
- Write down any error code shown on the indoor unit or thermostat. It speeds up the service visit.
When it is a real fault
Call for service if any of these happen:
- The outdoor coil stays encased in ice after a defrost cycle, or ice forms on top of the unit or the fan blades.
- The compressor runs but the outdoor fan never spins, outside of defrost.
- The system cools in summer but blows only cool air in heating mode for long periods.
- A breaker trips repeatedly, or you smell burning.
- Error codes keep returning after a reset.
Common causes include a failed defrost sensor or control board, low refrigerant from a leak, a stuck reversing valve, and blocked drainage that lets meltwater refreeze. If it is the middle of a cold night, our emergency HVAC repair guide covers what to do while you wait.
How to prevent cold-weather problems next winter
- Book service in the fall. A technician checks refrigerant pressures, defrost controls and drainage before the cold. See our heat pump maintenance guide and the fall HVAC checklist for Victoria homes.
- Raise the outdoor unit. A stand or wall bracket keeps it above snow and lets defrost water drain away.
- Keep it out from under drips. Water from a roof edge or failed gutter freezes on the unit. Fix the gutter or move the unit.
- Size for the whole house. If the system has never kept up on cold days, the problem may be capacity, not repair. Our comparison of ducted and ductless heat pumps explains how whole-home systems are sized for Victoria winters.
Not sure whether it is defrost or a fault? Contact us with what you are seeing and any error code, or see our repair and maintenance services.