A failed PCB (printed circuit board) in your heat pump's indoor unit is one of the more frustrating faults you can encounter — the unit may do nothing at all, behave erratically, or flash error codes with no obvious cause. The good news is there are several tell-tale signs you can look for before calling a technician, though the actual diagnosis and repair must be carried out by a qualified professional.
What Does the Indoor Unit PCB Actually Do?
The indoor unit PCB is essentially the brain of your heat pump's head unit. It controls the fan motor, the swing louvres, the thermistor readings (temperature sensors), communication with the outdoor unit, and the display panel. When it fails — whether from a power surge, moisture ingress, age, or a component fault — any one of these functions can be affected, or the unit may stop working entirely.
Common Signs the PCB May Have Failed
1. The Unit Won't Respond to the Remote or Buttons
If your heat pump shows no signs of life — no display, no beep, no fan movement — despite having power at the wall, a failed PCB is a strong possibility. First, check the circuit breaker and isolating switch haven't tripped. If power is confirmed and the unit is still completely unresponsive, the PCB is a likely culprit.
2. Persistent or Unusual Error Codes
Most modern heat pumps (Mitsubishi Electric, Fujitsu, Daikin, Panasonic, and others common in NZ) display fault codes on the indoor unit's display or via flashing LED patterns. Codes that relate to communication errors between the indoor and outdoor units, or sensor faults that don't clear after a reset, can point to PCB failure. Check your owner's manual for the specific code meanings — don't guess.
3. Erratic or Random Behaviour
The unit turns on and off by itself, the fan runs at the wrong speed, louvres move randomly, or the display shows garbled characters — these are classic signs of a PCB that is partially functioning but unreliable. This can also be caused by loose wiring or a failing capacitor on the board.
4. The Unit Runs But Doesn't Heat or Cool
If the fan runs but the compressor never starts, and the outdoor unit isn't receiving a signal, the PCB may not be sending the correct commands. This symptom overlaps with other faults (refrigerant issues, outdoor unit problems), so professional diagnosis is essential.
5. Visible Burn Marks or Smell
If you can safely remove the front panel (with the unit isolated from power at the wall isolating switch and the circuit breaker), look for obvious signs of damage: burn marks, discolouration, swollen capacitors, or a burnt smell. If you see any of these, do not attempt to operate the unit — call a technician immediately.
Safe DIY Checks You Can Do
Before concluding the PCB has failed, run through these basic checks:
| Check | What to Look For |
|---|---|
| Power supply | Circuit breaker tripped? Isolating switch off? |
| Remote control | Fresh batteries? Try the manual button on the unit |
| Error code | Note the code and look it up in your manual |
| Reset | Turn off at the isolating switch for 5 minutes, then restart |
| Wiring connections | Only inspect visually with power fully isolated |
A simple power reset (isolating the unit for several minutes) can sometimes clear a temporary fault. If the fault returns immediately or the unit still won't respond, the problem is likely hardware-related.
What You Cannot and Should Not Do
Do not attempt to test, repair, or replace the PCB yourself. Heat pump electrical work — including any work on internal wiring, control boards, or refrigerant circuits — is restricted electrical work under New Zealand law. It must be carried out by a registered electrician or a licensed heat pump technician. The Electrical Workers Registration Board (EWRB) maintains the register of licensed electrical workers. Unlicensed work is illegal, can void your warranty, and creates serious safety risks including fire and electrocution.
Refrigerant handling is also restricted under New Zealand law and must only be performed by a certified technician.
PCB Replacement: What to Expect
If a technician confirms PCB failure, they will typically source a replacement board from the manufacturer or an authorised parts supplier. Genuine parts are strongly recommended — aftermarket PCBs can cause compatibility issues. Costs vary significantly depending on the brand and model; as a rough guide, parts and labour for a PCB replacement can range from a few hundred dollars to over a thousand dollars for premium units. Always get a written quote before authorising work.
For units that are older (10+ years), your technician may advise that replacement of the entire indoor unit is more cost-effective than a PCB repair — worth discussing openly.
When to Call a Professional
Call a qualified heat pump installer or refrigeration technician if:
- The unit is completely unresponsive after basic checks
- You see burn marks, smell burning, or notice any physical damage to the board
- Error codes persist after a reset
- The unit behaves erratically or unpredictably
- You're unsure of anything — guessing with electrical components is never worth the risk
You can find qualified local heat pump installers and technicians on tradedirectory.co.nz. Look for technicians who are registered with the EWRB and experienced with your specific brand.
For general guidance on healthy indoor environments and heat pump use in NZ homes, Energywise is a useful resource. For building-related questions about heat pump installation compliance, refer to MBIE Building Performance.
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