- Most common cause
- Defrost cycle normal on frosty mornings
- Second most common
- Dirty filters a ten-minute fix
- Professional service, single unit
- $79–$249 typical per visit
A heat pump that suddenly feels cold is unsettling, especially mid-winter. Most of the time it is something you can check from the floor in a few minutes. Work through the list below in order: the first three cover most calls, and none of them needs tools.
Why is my heat pump blowing cold air in heating mode?
The usual reason is the defrost cycle. When it is cold and damp outside, ice builds up on the outdoor unit's coil. To clear it, the heat pump briefly reverses and sends warmth outside, so the indoor fan slows or stops and the air from the indoor unit can feel cool. You may see steam rising from the outdoor unit and water dripping under it. After a few minutes it switches back and the warm air returns.
Defrosting is a sign the unit is doing its job, not a fault. It happens more in inland and southern towns with hard frosts, and less in mild coastal places. If the air stays cold for much longer than that, or the outdoor unit stays iced over, go on to the checks below.
Why does my heat pump blow cold air when I first turn it on?
Most units hold the indoor fan back for a short time at start-up until the coil has warmed, so you don't get a blast of cold air. If the fan is set to a high fixed speed rather than auto, you may feel cool air before the heat arrives. Give it a few minutes on auto fan before deciding something is wrong.
What should I check before calling a technician?
Checks for a heat pump that isn't heating
- Check the mode
Look at the remote. It should show heat (often a sun symbol), not cool (a snowflake), dry (a water drop) or fan only. Auto mode can switch to cooling on a warm afternoon. Also replace the remote batteries if the display is faint.
- Check the set temperature
The set temperature has to be above the room temperature for the unit to heat. If it is set to 18°C and the room is already 19°C, it will just circulate air. Setting it to 30°C does not heat faster; see our winter settings guide.
- Clean the filters
Blocked filters starve the unit of air, and weak, lukewarm airflow is the classic sign. Lift the front panel, slide them out, vacuum and rinse. Our filter cleaning guide has the steps.
- Look at the outdoor unit
Clear leaves, long grass, firewood, bins and covers away from it. Air has to move freely through the coil. If it is caked in ice that does not clear after a defrost, switch off and call for a service.
- Check the timer and any eco or quiet mode
An off-timer, a weekly timer or a low-power mode can make it seem the unit has stopped heating. Cancel the timers and try again on a plain heat setting.
- Look for an error code
A flashing light or code on the indoor unit is the unit telling you it has detected a fault. Write the code down and look it up in your manual, or give it to the technician.
- Reset it once
Turn it off at the remote, then switch off power at the isolation switch for a few minutes and turn it back on. If a fault comes back after a reset, it needs a technician.
When is a heat pump that won't heat a job for a technician?
Once the mode, filters, outdoor unit and timers are ruled out, the remaining causes are inside the system and are not owner jobs. Refrigerant work in New Zealand must be done by a licensed technician, and the electrics by a registered electrical worker.
- The unit runs but the air never gets warm, even after an hour on heat.
- The outdoor unit stays iced over, or the outdoor fan doesn't spin.
- An error code keeps coming back after a reset.
- You hear new rattling, grinding or hissing.
- Heating has been getting weaker year on year, even with clean filters.
A service typically costs $79–$249 per visit for a single wall or floor unit. See heat pump servicing for what a proper service includes. If the unit is old and a major part such as the compressor has failed, compare the repair quote with a new installed unit using our replacement cost guide.
Could the heat pump simply be too small?
Yes, and it is common. A unit that copes in autumn but can't keep up on the coldest nights, while running flat out, is often undersized for the room, or the room has lost insulation, gained an open doorway, or been knocked through to another space. Our heat pump size calculator works out the kW the room actually needs, with the working shown.
Frequently asked questions
Why is my heat pump blowing cold air in heat mode?
Usually because it is defrosting the outdoor unit, which is normal on cold, damp days and lasts a few minutes. If the air stays cold, check the mode, set temperature, filters and outdoor unit, then call a technician.
How do I know if my heat pump is in defrost mode?
The indoor fan slows or stops, an indicator light may flash, and you may see steam and water coming from the outdoor unit. Warm air returns after a few minutes.
Why is my heat pump running but not heating the room?
Check that it is on heat rather than auto or cool, that the set temperature is above the room temperature, and that the filters are clean. A unit running flat out without warming the room may also be too small for the space.
Should I turn my heat pump off when it is defrosting?
No. Leave it alone. Switching off mid-defrost means the ice is still there next time it starts.
Can low refrigerant make a heat pump blow cold air?
It can, and it needs a licensed technician to find the leak and recharge it. That isn't something to try yourself.
Is it worth repairing an old heat pump that won't heat?
Consumer NZ gives heat pumps a life expectancy of 10 to 15 years. Near the end of that, or for a major fault like a compressor, a replacement often makes more sense than a repair. Get the repair quoted and compare.