A failing heat pump compressor is one of the most serious — and costly — faults your system can develop. The good news is that compressors rarely fail without warning. Knowing the early signs can save you from a complete breakdown, especially heading into a cold NZ winter or a humid summer.
What Does the Compressor Actually Do?
The compressor is the heart of your heat pump. It pressurises the refrigerant, allowing the system to move heat either into or out of your home. Without a working compressor, your heat pump simply cannot heat or cool. Most residential heat pumps in NZ use an inverter-driven scroll compressor, which varies its speed to match demand — making them efficient but also sensitive to certain faults.
Common Warning Signs of a Failing Compressor
Watch out for these tell-tale symptoms:
- Reduced heating or cooling output — The unit runs but the air coming out is barely warm (in heating mode) or barely cool (in cooling mode), even after allowing 10–15 minutes for the system to reach temperature.
- Unusual noises — Rattling, grinding, clanking, or a hard "clunk" on start-up can indicate worn bearings, loose internal components, or a compressor struggling to start.
- Hard starting or frequent tripping — If the outdoor unit hums loudly then shuts off, or if your circuit breaker trips repeatedly when the heat pump runs, the compressor may be drawing excessive current.
- The outdoor unit runs but indoor unit blows ambient air — This often points to the compressor not engaging at all.
- Error codes on the indoor unit display — Most modern heat pumps (Mitsubishi Electric, Daikin, Fujitsu, Panasonic, etc.) display fault codes. Check your owner's manual for what these mean; compressor-related codes are common.
- Ice build-up on the outdoor unit (outside of normal defrost cycles) — Can indicate low refrigerant caused by a leak, which puts extra strain on the compressor.
- Higher than usual power bills — A struggling compressor works harder and draws more electricity to achieve the same result.
What You Can Safely Check Yourself
Before calling a technician, run through these basic checks:
| Check | What to look for |
|---|---|
| Air filters | Blocked filters restrict airflow and stress the compressor — clean them monthly |
| Outdoor unit clearance | Ensure nothing is blocking airflow around the outdoor unit (at least 30 cm clearance is typical) |
| Circuit breaker | Check it hasn't tripped; reset once and observe |
| Remote/controller settings | Confirm the mode and set temperature are correct |
| Error code | Note any code shown on the display and look it up in your manual |
Cleaning your filters is straightforward and something every homeowner should do regularly. Beyond this, do not attempt to open the outdoor unit, handle refrigerant, or tamper with electrical components — this is both dangerous and, in NZ, legally restricted work.
What Is Restricted Work — and Why It Matters
In New Zealand, handling refrigerants is controlled under NZ ozone protection legislation and requires a certified technician. Electrical work on heat pump wiring is restricted electrical work under the Electricity Act, meaning it must be carried out by a registered electrician or authorised person. You can find registered electrical workers through the Electrical Workers Registration Board.
Attempting DIY repairs on the refrigerant circuit or internal electrics is illegal, potentially dangerous, and will void your warranty.
How a Technician Diagnoses a Failing Compressor
A qualified heat pump technician will typically:
- Check refrigerant pressures using manifold gauges — low suction pressure often points to a leak or compressor fault.
- Measure compressor amp draw — if it's drawing significantly more current than rated, the compressor is struggling.
- Test compressor windings with a multimeter for shorts or open circuits.
- Check for compressor "burnout" — a burnt smell and contaminated oil are clear indicators.
- Review system error logs stored in the control board.
Repair or Replace?
Compressor replacement is expensive — often $1,500–$3,500+ as a rough guide depending on the unit size and brand, though costs vary widely. For older units (10+ years), a full heat pump replacement may be more cost-effective. Your technician can advise based on the age, refrigerant type, and overall condition of your system. Units using older refrigerants like R22 are particularly worth replacing, as R22 is being phased out globally.
For guidance on energy-efficient replacement options, Energywise has useful NZ-specific advice on heat pump selection.
NZ Climate Considerations
NZ's varied climate — from the cold, damp South Island to the humid upper North Island — puts different stresses on heat pumps. In colder regions, compressors work harder in winter and are more prone to wear. Regular servicing (at least annually) is strongly recommended and aligns with guidance from BRANZ on maintaining building services.
If your heat pump is covered under the Healthy Homes Standards (relevant for rental properties), a non-functioning heat pump may put you in breach of your obligations. Check Tenancy Services for landlord requirements.
When to Call a Professional
Call a licensed heat pump technician if you notice:
- Any of the warning signs listed above that persist after basic checks
- Error codes you cannot resolve by resetting the unit
- Unusual smells (burning or chemical odours) from either unit
- The circuit breaker tripping more than once
- Any visible damage to wiring or the outdoor unit
A qualified installer or refrigeration technician can diagnose the problem accurately and carry out repairs safely and legally. You can find experienced local heat pump technicians on tradedirectory.co.nz.
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