CH35 on a LG heat pump: Low pressure error – evaporating pressure excessively low
Short answer
On a LG heat pump, CH35 means: Low pressure error – evaporating pressure excessively 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: Low pressure error – evaporating pressure excessively low.
Part involved: refrigerant circuit low side.
When it shows: Low pressure below limit.
Likely causes:
- Low pressure sensor defect; outdoor fan fault; refrigerant shortage/leakage; refrigerant pipe damage/deformation; EEV fault or strainer blockage/freezing; outdoor heat exchanger blocked (ice, debris) or indoor filter clogged in cooling; service valve closed; outdoor PCB defect; pipe sensor failure.
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
- Inspect fan, EEV and strainers (temperature difference/freezing), check for leaks, compare manifold with LP sensor, correct charge; do not replace PCB before EEV inspection (LG).
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
- AIR-TO-WATER HEAT PUMP SERVICE MANUAL (General) – R32 Hydrosplit, MFL68682007 ↗ · MFL68682007 · page 72, 114 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026