CH23 on a LG heat pump: DC link voltage low or high – inverter DC-link not charging or outside limits
Short answer
On a LG heat pump, CH23 means: DC link voltage low or high – inverter DC-link not charging or outside limits. 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: DC link voltage low or high – inverter DC-link not charging or outside limits.
Part involved: inverter PCB DC link.
When it shows: DC link voltage above 420 V DC or below 140 V DC (R290/Monobloc S installer manuals); Gen1 TS: above 480 V / below 140 V.
Likely causes:
- Incorrect DC-link wiring / loose terminal; capacitor burnout; inverter PCB DC-link detection part burnout; abnormal input voltage (R,S,T,N); missing N phase; S-phase fuse blown; input voltage distortion or heavy load on same supply.
On the THERMA V Water Heater (heat pump DHW cylinder)
The manual says: DC link low/high voltage (THERMA V water heater).
Part involved: inverter PCB / compressor.
When it shows: DC link low/high voltage.
Likely causes:
- DC link low/high voltage.
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
- 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.
On the THERMA V Water Heater (heat pump DHW cylinder)
- 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 with LG Therma V training; F-gas certified refrigeration engineer for refrigerant-circuit work.
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, 103-106, 109 · 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