If your heat pump is running but the room temperature isn't budging, don't panic — this is one of the most common heat pump complaints in New Zealand homes. In many cases, the fix is straightforward and something you can tackle yourself. However, some causes do require a licensed refrigeration technician, so it's important to know the difference.
Start With the Basics: Settings and Remote
Before pulling the unit apart, check the obvious first:
- Mode setting: Make sure the unit is set to Heat (not Fan or Dry) in winter, or Cool in summer. It sounds simple, but incorrect mode selection is a surprisingly common culprit.
- Set temperature: Is the target temperature actually different from the current room temperature? If the room is already at the set point, the heat pump will run the fan but won't actively heat or cool.
- Remote control batteries: Weak batteries can cause the remote to send incomplete signals, leaving the unit in the wrong mode or at the wrong temperature.
- Timer settings: Check whether an active timer is overriding your manual settings.
Check and Clean the Air Filters
Dirty filters are the single most common reason a heat pump runs without effectively changing room temperature. When filters are clogged, airflow is severely restricted and the unit simply can't move enough conditioned air into the room.
How to clean filters:
- Turn the unit off at the wall.
- Open the front panel of the indoor unit (it usually clips open).
- Slide out the mesh filters.
- Vacuum off loose dust, then rinse under warm water.
- Allow to dry completely before reinserting — never run the unit with wet filters.
Most manufacturers recommend cleaning filters every 4–6 weeks during heavy use. This simple step can dramatically improve performance and is covered in detail in guidance from BRANZ on maintaining home heating systems.
Inspect the Outdoor Unit
The outdoor unit (condenser) needs clear airflow to work properly. Walk outside and check:
- Blocked airflow: Is the unit surrounded by overgrown shrubs, stored items, or debris? Clear at least 300–500 mm of space around it.
- Ice or frost build-up: In cold weather, some frost on the outdoor unit is normal — the unit will periodically run a defrost cycle. However, a solid block of ice indicates a problem (see below).
- Dirty coils: Visible dirt or leaf matter on the outdoor coil fins can reduce efficiency significantly. A gentle rinse with a garden hose (unit off at the isolator switch) can help, but avoid high-pressure water.
Look for Error Codes
Most modern heat pumps display error or fault codes on the indoor unit's display panel or via flashing indicator lights. Check your owner's manual to decode these — they can point directly to the fault. Common codes relate to refrigerant issues, sensor faults, or communication errors between indoor and outdoor units.
Possible Causes That Need a Professional
Some causes of poor heating or cooling performance are not DIY-fixable and require a licensed refrigeration and air conditioning technician:
Low or Leaking Refrigerant
Refrigerant (the gas that actually transfers heat) can leak over time. A unit low on refrigerant will run continuously but barely change room temperature. Handling refrigerants is restricted work under NZ law — only licensed technicians are permitted to handle, recover, or recharge refrigerants under the Ozone Layer Protection Act. Do not attempt this yourself.
Faulty Compressor
The compressor is the heart of the system. If it's failing, the unit will run but won't effectively heat or cool. This is a significant repair best assessed by a professional.
Sensor or Control Board Faults
A faulty thermistor (temperature sensor) can cause the unit to misread room temperature and behave erratically. Diagnosing and replacing sensors requires technical knowledge and tools.
Undersized Unit for the Space
If your heat pump has always struggled to heat or cool the room, it may simply be undersized for the space. NZ homes vary widely in insulation levels, ceiling height, and glazing — all of which affect the required heat pump capacity. Energywise has useful guidance on sizing heat pumps correctly for NZ conditions.
Quick Diagnostic Table
| Symptom | Likely Cause | DIY Fix? |
|---|---|---|
| Fan runs, no heating/cooling | Wrong mode or set temp | Yes |
| Weak airflow from indoor unit | Dirty filters | Yes |
| Outdoor unit iced over completely | Low refrigerant or airflow issue | No — call a tech |
| Error code on display | Varies by code | Check manual first |
| Unit runs constantly, no effect | Low refrigerant or faulty compressor | No — call a tech |
| Room too large for unit | Undersized system | Consult installer |
Healthy Homes and Rental Properties
If you're a landlord, note that the Tenancy Services Healthy Homes Standards require rental properties to have a fixed heating device capable of heating the main living room to at least 18°C. A heat pump that isn't performing correctly may put you in breach of these standards, so prompt repair is important.
When to Call a Professional
Call a qualified heat pump technician if:
- You've checked filters, settings, and airflow and the problem persists.
- You see a complete ice block on the outdoor unit.
- The unit is displaying a fault code you can't resolve.
- You suspect a refrigerant leak (signs include hissing sounds, ice on pipework, or a sudden drop in performance).
- The unit is more than 10 years old and performance has gradually declined.
Refrigerant handling and electrical work inside the unit are restricted work under NZ law. Attempting these yourself is illegal and dangerous. You can find qualified local heat pump installers and technicians on tradedirectory.co.nz.
ISO 9001
