CH25 on a LG heat pump: Inverter input voltage too high or too low
Short answer
On a LG heat pump, CH25 means: Inverter input voltage too high or too low. 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: Inverter input voltage too high or too low.
Part involved: mains supply / inverter PCB.
When it shows: Inverter input voltage outside 173-289 V for 4 s (High Temperature manual).
Likely causes:
- Supply voltage outside unit limits.
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
- Isolate and wait at least 3 minutes for DC-link capacitors to discharge. Check supply voltage (1ph 230 V ±15 %, 3ph 400 V ±15 %), outdoor fan free to rotate and heat exchanger unobstructed, service valves open, EEV operation, refrigerant charge/pressures (LGMV), compressor U-V-W wiring, winding resistance and insulation resistance, IPM/IGBTM diode test, then replace inverter PCB or compressor as indicated by LGMV fault-finding.
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
- LG Therma V AHBW A0 Series Service Manual (R410A Monobloc AHBW036H0, AHBW056A0…AHBW168A0), P/No. MFL58346405 (April 2013) – ManualsLib 3030181 ↗ · P/No. MFL58346405 · page 48 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026