CH55 on a LG THERMA V R290 Monobloc: Modbus communication error (Modbus ↔ indoor PCB) – R290 Monobloc
Short answer
On a LG heat pump, CH55 means: Modbus communication error (Modbus ↔ indoor PCB) – R290 Monobloc. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Modbus communication error (Modbus ↔ indoor PCB) – R290 Monobloc.
Part involved: Modbus interface.
When it shows: Loss of Modbus communication.
Likely causes:
- Listed in R290 installer manual with note "Not applicable to this model?" – likely Modbus/third-party controller interface loss.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
Resetting itself: yes – trouble clears when the condition is repaired; emergency operation must be restarted by the user after a power reset.
Manual reset: Not normally required; user restarts after power reset if emergency operation was running.
What you can check
- Read the code on the controller (LG shows 'CH' + number; older wired controllers alternate 'CH' and the number) and note it together with the model number. Report it to your installer or an LG-authorised service centre – LG owner's manuals say an error code generated by self-diagnosis is a reason to call the service. For this 'trouble' class LG allows temporary emergency operation: if the controller shows a pop-up offering it you may accept (OK) as a stop-gap; running costs will be higher, so do not use it long term. Emergency operation does not restart by itself after a power cut – you must switch it back on at the controller.
What the engineer will check
- Check Modbus wiring/addressing of third-party controller or gateway and indoor PCB.
Who to ask for: Heat pump engineer (controls, sensors, PCB).
Certification: None statutory beyond electrical competence (BS 7671).
What you might notice
What owners and engineers report
1 owner and engineer report mentions this.
- Controller / thermostat problem on the THERMA V R290 Monobloc: 1 report
Sources
- LG THERMA V R290 Monobloc Installation Manual (HM..HF UB60 / UB40, PHCS0), MFL68681848 Rev.03 (2024) – ManualsLib 3668662 ↗ · MFL68681848 Rev.03_112224 · page 182 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026