H06.78 on a Baxi HP60 / Baxi Assure HP55 High Temperature Monobloc ASHP: ODU internal com Err Communication error between refrigerant system and hydronic system main control boards
Short answer
On a Baxi heat pump, H06.78 means: ODU internal com Err Communication error between refrigerant system and hydronic system main control boards. 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: ODU internal com Err Communication error between refrigerant system and hydronic system main control boards.
Part involved: PCB communication wiring.
Likely causes:
- The cable is not connecting the main PCB B and the main control PCB of the hydraulic module. Connect the cable. The communication cable order is incorrect. Reconnect the cables in the correct order. There is significant magnetic or electrical interference caused by lifts, large electrical transformers, etc. Add shielding to protect the unit or move the unit.
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 - system restarts automatically when the cause disappears (may run in degraded/back-up mode meanwhile).
Manual reset: not required once cause removed.
What you can check
- Note the exact code shown on the controller and when it appeared.
- The manual's user steps allow switching the system off and on once to see if the error clears; if the code returns, contact the installer.
- If the code persists or returns, contact a heat pump engineer.
What the engineer will check
- The cable is not connecting the main PCB B and the main control PCB of the hydraulic module. Connect the cable. The communication cable order is incorrect. Reconnect the cables in the correct order. There is significant magnetic or electrical interference caused by lifts, large electrical transformers, etc. Add shielding to protect the unit or move the unit.
Who to ask for: heat pump engineer (controls / sensors).
Certification: Manufacturer-trained heat pump engineer.
What you might notice
Sources
- Installation, user and service manual - Indoor unit ASHP Control ↗ · 7887625 - v04 - 22072025 · page 133 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026