CH36 on a LG THERMA V High Temperature Split: Low pressure ratio error of inverter compressor – outdoor unit (R410A stage) error on High Temperature split; shown on outdoor 7-segment LED with unit number suffix (e.g. "36 1") and on the indoor display/remote controller
Short answer
On a LG heat pump, CH36 means: Low pressure ratio error of inverter compressor – outdoor unit (R410A stage) error on High Temperature split; shown on outdoor 7-segment LED with unit number suffix (e.g. "36 1") and on the indoor display/remote controller. 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: Low pressure ratio error of inverter compressor – outdoor unit (R410A stage) error on High Temperature split; shown on outdoor 7-segment LED with unit number suffix (e.g. "36 1") and on the indoor display/remote controller.
Part involved: outdoor unit (R410A stage).
When it shows: High/low pressure ratio maintained below 1.8 for 3 min or more.
Likely causes:
- High/low pressure ratio maintained below 1.8 for 3 min or more.
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 (without opening any panels) that the outdoor unit is not blocked by leaves, debris, snow or ice and that nothing is stacked against the coil or fan grille.
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 with LG Therma V training; F-gas certified refrigeration engineer for refrigerant-circuit work.
Certification: F-gas certification (UK F-gas Regulation, Category I) for any refrigerant handling on R32/R410A units; for R290 units additionally competence in flammable (hydrocarbon) refrigerants (e.g. BESA/ACRIB HC safe handling).
What you might notice
Sources
- LG THERMA V High Temperature Installation Manual (AHUW166T3 / AHNW166T3 cascade R410A/R134a), MFL67212828 Rev.00 (2019) – ManualsLib 1770589 ↗ · MFL67212828 Rev.00_051519 · page 121-122 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026