170 on a Mitsubishi Heavy Industries Air-Conditioning Europe Hydrolution: Communication fault with PCA input: Communication fault has occurred to the input board AA3
Short answer
On a Mitsubishi Heavy Industries Air-Conditioning Europe heat pump, 170 means: Communication fault with PCA input: Communication fault has occurred to the input board AA3. The heat pump keeps running.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Communication fault with PCA input: Communication fault has occurred to the input board AA3.
Part involved: Communication fault with PCA input.
When it shows: Communication fault has occurred to the input board AA3.
Likely causes:
- Check the communication cables and their connections.
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Severity | Information only |
| Engineer needed? | No |
The heat pump keeps running.
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