CH54 on a LG heat pump: Open-phase / reverse-phase (R-S-T) error – mains wiring fault on 3-phase models
Short answer
On a LG heat pump, CH54 means: Open-phase / reverse-phase (R-S-T) error – mains wiring fault on 3-phase models. 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: Open-phase / reverse-phase (R-S-T) error – mains wiring fault on 3-phase models.
Part involved: mains supply (3-phase).
When it shows: Phase sequence incorrect or phase missing (3-phase models only).
Likely causes:
- Main power wiring fault: reverse phase, missing N phase or phase loss; fuse damage (R,S phase); inverter PCB fault.
Is it safe?
Switch the heat pump off at its isolator and call an engineer.
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
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. Check the heat pump's breaker/isolator at the consumer unit is on; if a breaker or RCD has tripped, do not keep resetting it – leave it off and call an engineer.
What the engineer will check
- Measure R-S-T-N voltages (230 V phase-N, 400 V phase-phase), check phase sequence and fuses, swap R and S if reversed; check inverter PCB.
Who to ask for: Heat pump engineer / electrician (inverter and PCB diagnostics).
Certification: Competent person for electrical work (BS 7671); isolate and wait 3 min for DC-link discharge.
What you might notice
Sources
- AIR-TO-WATER HEAT PUMP SERVICE MANUAL (General) – R32 Hydrosplit, MFL68682007 ↗ · MFL68682007 · page 72, 118-119 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026