CH05 on a LG heat pump: Communication error between indoor unit Main PCB and outdoor unit (Main PCB(Outdoor cycle)/inverter PCB) – indoor does not receive the outdoor signal
Short answer
On a LG heat pump, CH05 means: Communication error between indoor unit Main PCB and outdoor unit (Main PCB(Outdoor cycle)/inverter PCB) – indoor does not receive the outdoor signal. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 2 sources
What it means
On the LG, all models
The manual says: Communication error between indoor unit Main PCB and outdoor unit (Main PCB(Outdoor cycle)/inverter PCB) – indoor does not receive the outdoor signal.
Part involved: indoor–outdoor communication cable / PCBs.
When it shows: No communication between Main PCB(Indoor) and Main PCB(Outdoor cycle) for 3 minutes or more (R290 TS guide).
Likely causes:
- Transmission connector disconnected; connecting wires misconnected or broken; outdoor Main/Inverter PCB abnormal; indoor Main PCB abnormal; incompatible software versions; noise; abnormal input voltage/earth.
On the THERMA V Water Heater (heat pump DHW cylinder)
The manual says: PCB communication error (THERMA V water heater).
Part involved: PCB / controls.
When it shows: PCB communication error.
Likely causes:
- PCB communication error.
Is it safe?
On the LG, all models
| 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.
On the THERMA V Water Heater (heat pump DHW cylinder)
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Resetting itself: unknown.
Manual reset: Per LG corrective action; service engineer for most codes.
What you can check
On the LG, all models
- 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.
On the THERMA V Water Heater (heat pump DHW cylinder)
- Note the code shown on the water heater display. LG's corrective action: call LG technical support. While the fault is present the unit operates as: Use elements only – hot water will be heated more slowly/at higher cost.
What the engineer will check
On the LG, all models
- 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 CH05 check the outdoor Main PCB first, then the indoor Main PCB. Check L-N 207-254 V / 3ph 357-440 V.
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.
On the THERMA V Water Heater (heat pump DHW cylinder)
- Check PCB connections/communication and anode (ICCP) circuit; replace PCB/anode controller as required.
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 71, 82-83 · Reviewed 23 September 2026
- LG Heat Pump Water Heater Owner's Manual WH20S F5 / WH27S F5 (EU/UK multilingual), MFL71409209 Rev.00 (2023) – ManualsLib 3195149 ↗ · MFL71409209 Rev.00_090823 · page 32 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026