CH53 on a LG heat pump: Communication error: outdoor unit fails to receive signal from indoor unit (Main PCB(Indoor) → Main PCB(Outdoor))
Short answer
On a LG heat pump, CH53 means: Communication error: outdoor unit fails to receive signal from indoor unit (Main PCB(Indoor) → Main PCB(Outdoor)). 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: Communication error: outdoor unit fails to receive signal from indoor unit (Main PCB(Indoor) → Main PCB(Outdoor)).
Part involved: indoor–outdoor communication.
When it shows: Outdoor does not receive IDU signal.
Likely causes:
- Communication cable broken/miswired/polarity; indoor PCB damaged; incompatible software versions; noise; power supply problems.
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 – 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
- Check the communication cable terminations and polarity between the named PCBs, look for intermediate twisted joints, shorts or open circuits, check for noise sources near the cable, confirm supply voltage and earthing, check software/EEPROM versions of both PCBs are compatible, then replace the defective PCB. LG: for CH53 check the indoor Main PCB first, then the outdoor Main 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, 82-83 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026