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A heat pump technician diagnoses the fault, whether it lies in the defrost controls, the reversing valve, the fans, the refrigerant circuit or the thermostat settings, then repairs it and checks that the system heats, defrosts and switches to backup the way it should. Refrigerant and high-voltage work must be done by a certified technician, and releasing refrigerant is prohibited.
Some of what worries homeowners is perfectly normal, like steam rising from the unit during defrost or air that feels cooler than a furnace's. This page explains how to tell normal winter behaviour from a real problem, the most common cold-weather failures, what to do if the heat pump stops heating, what a repair visit covers and the maintenance that keeps breakdowns away.
Signs your heat pump needs repair
- The outdoor unit stays coated in ice for hours, or ice keeps building until it covers the top or sides of the cabinet.
- The heat pump never seems to go into defrost, or it defrosts so often that the house can't stay warm.
- The electric backup or the furnace runs far more than usual in weather the heat pump normally handles on its own.
- Your electricity bills climb noticeably with no change in the weather or in your habits.
- Cool air blows from the registers for long stretches, not just during short defrost cycles.
- The outdoor fan or compressor doesn't start, or the unit trips its breaker.
- The heat pump heats but won't switch to cooling in summer, or the reverse, which points to the reversing valve or its controls.
- An error code flashes on the indoor unit, the thermostat or the outdoor unit's control board.
Heat pump defrost cycles: what's normal in winter
When the outdoor temperature is near or below freezing, moisture in the air freezes on the outdoor coil as the heat pump draws heat from it. To clear that frost, Natural Resources Canada explains, the heat pump briefly switches to cooling mode to send hot refrigerant through the outdoor coil, and stops the outdoor fan while the frost melts. Defrost is triggered either by controls that sense frost building up or at preset intervals, which NRCan gives as 30, 60 or 90 minutes.
That process has visible side effects that are not breakdowns: a cloud of steam over the unit, a whoosh or click as the reversing valve shifts, a silent outdoor fan and water running off the coil. During defrost the heat pump is actually cooling the air in the ducts, so backup heat usually comes on to temper it. If cool drafts during defrost bother you, NRCan notes that the installer can set the indoor fan to stop during defrost, although each cycle may then take a little longer.
Common heat pump problems in cold weather
- A failed defrost sensor, defrost control board or reversing valve lets ice build on the outdoor coil until the unit can barely heat.
- A blocked drain path, or a unit sitting too low, lets defrost water refreeze underneath and creep back up into the coil.
- Drifting snow, or ice falling from a roof edge, can bury the outdoor unit or bend its fan blades and fins.
- A refrigerant leak reduces heating output, leaves patchy frost on the coil and makes the backup heat run more.
- The outdoor fan motor, its capacitor or a contactor can fail, stopping the outdoor unit while the indoor fan keeps blowing.
- A thermostat or control set up incorrectly can call for backup heat too early, or never call for it at all.
- Ductless indoor units with clogged filters or dirty coils lose heating output and may shut down with a protective error.
What to do when your heat pump stops heating in winter
If the heat pump quits during a cold snap, the priority is keeping the house warm. Many thermostats let you switch to emergency or auxiliary heat, which runs only the furnace or the electric elements; use it until the technician arrives, knowing it costs more to run. If the outdoor unit is encased in ice, leave it off and don't chip at the ice with a tool or scraper, since the fins and coil are easily damaged.
- Check that the thermostat is set to heat and that the breakers for the outdoor unit, the air handler and the backup heat are all on.
- Shovel away snow banked against the outdoor unit and brush soft snow off its top by hand, leaving hard ice for the technician.
- Replace a dirty filter, since weak airflow also cuts heating output.
- If the house starts cooling down, close the doors of unused rooms and use only certified space heaters, kept well away from anything that can burn.
- When you call, say whether the outdoor unit is iced up, whether an error code is showing and whether the backup heat is working.
What a heat pump repair technician checks
A heat pump has more to its controls than an air conditioner, because it has to switch between heating, cooling and defrost. The technician reads any error codes, then tests the defrost sensor and control board, the reversing valve and its solenoid, the outdoor fan motor and capacitor, and the contactor. They measure refrigerant pressures and temperatures in heating mode and check the airflow across the indoor coil or through the ductless units.
They also look at how the backup heat is set up: the outdoor temperature at which it is allowed to start, whether it comes on in the right stages and whether the thermostat is actually configured for a heat pump. Refrigerant work, such as finding and repairing a leak or replacing a reversing valve, must be done by a certified technician who recovers the refrigerant instead of venting it.
Heat pump maintenance that heads off winter breakdowns
- Book the annual service that Natural Resources Canada recommends in early fall, so the defrost controls, electrical parts and refrigerant circuit are checked before the cold arrives.
- Change or clean the central filter every 3 months, as NRCan advises, and wash the filters of ductless indoor units as often as the manual calls for.
- Keep the stand or bracket clear so the unit stays above the snow and defrost water can drain away freely.
- Trim shrubs back and keep fallen leaves out of the coil in the fall.
- Avoid deep night-time setbacks: NRCan suggests limiting them to no more than 2°C, or using a smart thermostat that starts recovering early, because heat pumps respond slowly.
- With electric backup heat, NRCan recommends setting the backup's set-point 2°C to 3°C below the heat pump's so the heat pump does most of the work.
Heat pump repair or replacement: what to consider
Most heat pump repairs, such as a defrost sensor, a capacitor, a fan motor or a control board, are worth doing on a unit in reasonable shape. Replacement deserves a closer look when the compressor fails on an older unit, when leaks keep coming back, or when an older model that wasn't designed for cold climates leaves most of the winter heating to the backup system.
If you do replace it, the new heat pump should be sized from a fresh heating calculation rather than matched to the old unit, and a cold-climate model may carry much more of the winter load. Check the incentive programs in force where you live before signing, since some require an energy evaluation or specific equipment.
Heat Pump Repair: frequently asked questions
Why is my heat pump blowing cold air in winter?
Some of it is normal. Natural Resources Canada notes that heat pumps deliver more air at a lower temperature, typically between 25 and 45°C, compared with 55 to 60°C from a furnace, so the air can feel cool on your hand. Brief cool air during defrost is also expected. Cool air for long periods, with the house losing temperature, calls for a technician.
Is it normal for my heat pump to have ice on it?
A light, even layer of frost on the outdoor coil is normal in cold, damp weather, and the defrost cycle should clear it regularly. Thick ice that covers the coil for hours, ice on the top or the fan, or a solid block underneath the unit means defrost or drainage isn't working and needs service.
Why is steam coming out of my heat pump?
It is almost always the defrost cycle. Warm refrigerant melts the frost on the outdoor coil, and in cold air the meltwater gives off visible vapour for a few minutes. Smoke with a burning smell is different: turn the system off at the breaker and call for service.
What does emergency heat mean on my thermostat?
Emergency heat shuts off the heat pump and runs only the backup, whether a furnace or electric elements. It is meant for when the heat pump has failed or is waiting for repair, not for everyday use, since running the backup alone usually costs more.
Why does my auxiliary heat seem to run all the time?
In very cold weather it may simply be doing its job, because every heat pump loses capacity as it gets colder. It also runs more after a deep setback or when the controls are set to bring it in too early. If it runs constantly in milder weather, a technician should check the refrigerant charge, the defrost controls and the thermostat configuration.
Should I turn my heat pump off when it's extremely cold?
Usually not. Natural Resources Canada explains that each air-source heat pump has a cut-off temperature below which it stops operating, and a properly configured system switches to the backup on its own. Turning it off manually only makes sense if the unit is iced up, making unusual noises or showing an error.
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Written by the LokalMatch editorial team. Reviewed by Zubair Afzal on September 10, 2026. How we write and check our guides