171 on a Mitsubishi Heavy Industries Air-Conditioning Europe Hydrolution: Communication fault with PCA base: A temporary communication fault has occurred to PCB AA2
Short answer
On a Mitsubishi Heavy Industries Air-Conditioning Europe heat pump, 171 means: Communication fault with PCA base: A temporary communication fault has occurred to PCB AA2. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Communication fault with PCA base: A temporary communication fault has occurred to PCB AA2.
Part involved: Communication fault with PCA base.
When it shows: A temporary communication fault has occurred to PCB AA2.
Likely causes:
- Check the communication cables and their connections.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: yes.
Manual reset: no.
What you can check
- Note the alarm number/text shown on the display. Check the consumer-unit breakers/isolators for the indoor and outdoor units are on. This is an information message; it resets automatically when the cause is removed.
What the engineer will check
- Per manual 'May be due to': Check the communication cables and their connections. Check communication cabling, DIP switches and power to accessory/boards.
Who to ask for: Heat pump / refrigeration engineer (manufacturer-trained).
Certification: F-gas certification for refrigerant-circuit work; electrical competence (Part P/18th Edition) for PCB/wiring.
What you might notice
Sources
- Installation Manual - Air to Water Heat Pump using R32 refrigerant, Hydrolution (HM) ↗ · PSC012D169 (202201) · page PDF p.86 (printed 84) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026