191 on a Mitsubishi Heavy Industries Air-Conditioning Europe Hydrolution: Com. err. PCA accessory: Communication fault has occurred - hot water comfort
Short answer
On a Mitsubishi Heavy Industries Air-Conditioning Europe heat pump, 191 means: Com. err. PCA accessory: Communication fault has occurred - hot water comfort. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Com. err. PCA accessory: Communication fault has occurred - hot water comfort.
Part involved: Com. err. PCA accessory.
When it shows: Communication fault has occurred - hot water comfort.
Likely causes:
- Defective communication cables; accessory activated in display but not connected; incorrectly connected communication cable; incorrectly set DIP switch; no electrical supply to the accessory board.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
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': Defective communication cables; accessory activated in display but not connected; incorrectly connected communication cable; incorrectly set DIP switch; no electrical supply to the accessory board. 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.87 (printed 85) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026