A heat pump that keeps turning itself off — a problem known as short cycling — is one of the most common complaints NZ homeowners have. The good news is that several of the most likely causes are straightforward to check yourself, though some will need a qualified technician. Here's how to work through the problem systematically.
What Is Short Cycling?
Short cycling is when your heat pump starts up, runs for only a few minutes, then shuts off before your room reaches the set temperature — and then repeats the cycle. It wastes energy, puts extra wear on the compressor, and leaves your home uncomfortable. Identifying the root cause early can save you a costly repair bill.
Check the Air Filter First
A clogged air filter is the single most common reason a heat pump shuts down prematurely. When airflow is restricted, the unit overheats (in heating mode) or the evaporator coil freezes over (in cooling mode), and the system's safety controls shut it down to protect the compressor.
What to do:
- Turn the unit off at the remote or wall controller.
- Remove the indoor unit's front panel and slide out the filter.
- Rinse it under warm water, let it dry completely, and reinstall it.
- Most manufacturers recommend cleaning filters every 4–6 weeks during heavy use.
Check your owner's manual for the correct procedure for your brand.
Look for Ice Build-Up on the Indoor or Outdoor Unit
If you can see ice forming on the indoor coil or on the outdoor unit's fins, the system is likely going into a protective shutdown. Ice build-up can be caused by:
- A dirty filter (see above)
- Low refrigerant charge
- Blocked or restricted airflow around the outdoor unit
- Outdoor temperatures below the unit's rated operating range
What to do:
- Clear any debris, vegetation, or snow from around the outdoor unit — keep at least 300–500 mm of clearance on all sides.
- Turn the unit off and let it defrost naturally (do not use a heat gun or sharp objects).
- If icing returns after cleaning the filter and clearing the outdoor unit, call a technician — low refrigerant requires a licensed professional to diagnose and recharge.
Check the Remote Control and Settings
Sometimes the fix is simpler than you think:
- Sleep or timer mode: Many remotes have a sleep timer or auto-off function that can be accidentally activated. Check your remote settings.
- Set temperature already reached: If the room hits the target temperature, the unit will cycle off — this is normal behaviour. Try raising or lowering the set point to confirm.
- Auto mode confusion: In 'Auto' mode, some units switch between heating and cooling and may appear to shut off. Try switching to a fixed 'Heat' or 'Cool' mode.
Inspect the Outdoor Unit
The outdoor unit needs adequate airflow to operate correctly. Check for:
- Leaves, dirt, or debris blocking the coil fins
- Fences, garden structures, or plantings too close to the unit
- The unit sitting in direct recirculated airflow from another appliance
Gently rinse the outdoor coil fins with a garden hose (low pressure, top to bottom) if they look dirty. Avoid bending the fins.
Consider the Age and Condition of the Unit
Heat pumps typically last 15–20 years with good maintenance. Older units may short cycle due to:
- Worn or faulty capacitors — these help start the compressor and fan motors
- Failing thermistors or sensors — temperature sensors that give incorrect readings
- Compressor wear — an ageing compressor may overheat and trigger thermal protection
These faults require a qualified heat pump technician to diagnose with proper tools.
Electrical Supply Issues
Voltage fluctuations or an undersized circuit can cause a heat pump to shut down. If your lights dim when the unit starts, or if the circuit breaker trips, stop using the unit and call a licensed electrician. All electrical work on heat pump circuits is restricted work under NZ law and must be carried out by a registered electrician — see the Electrical Workers Registration Board (EWRB) for more information.
Refrigerant and Gas Issues
If you suspect a refrigerant leak (signs include reduced heating/cooling performance, hissing sounds, or ice on the indoor coil), do not attempt to handle this yourself. Refrigerant handling is restricted to licensed technicians under NZ regulations. A qualified installer will pressure-test the system, locate any leak, repair it, and recharge the refrigerant to the manufacturer's specification.
When to Call a Professional
Call a qualified heat pump installer or HVAC technician if:
- The unit continues short cycling after you've cleaned the filter and cleared the outdoor unit
- You notice ice build-up that returns after defrosting
- The outdoor unit makes unusual grinding, rattling, or hissing noises
- The circuit breaker trips when the unit runs
- The unit is more than 10 years old and performance has declined
- You suspect a refrigerant leak
A licensed installer can carry out a full system check, including refrigerant pressure testing, electrical checks, and sensor calibration. You can find qualified local heat pump installers on tradedirectory.co.nz.
For rental properties, landlords should also be aware that heating requirements under the Healthy Homes Standards may apply — a faulty heat pump that can't maintain temperature could put you in breach of your obligations.
Preventive Maintenance Tips
| Task | Frequency | Who Does It |
|---|---|---|
| Clean indoor filter | Every 4–6 weeks (heavy use) | Homeowner |
| Clear outdoor unit surrounds | Every season | Homeowner |
| Professional service & check | Annually | Licensed technician |
| Refrigerant pressure check | Every 2–3 years or if suspected | Licensed technician |
Regular servicing is the best way to prevent short cycling and extend the life of your unit. BRANZ provides good general guidance on maintaining home heating systems.
ISO 9001
