bc34 on a LG THERMA V High Temperature Split: Excessive rise of high pressure of inverter compressor – indoor-unit (R134a stage) inverter PCB error, displayed with prefix "bc" (High Temperature split)
Short answer
On a LG heat pump, bc34 means: Excessive rise of high pressure of inverter compressor – indoor-unit (R134a stage) inverter PCB error, displayed with prefix "bc" (High Temperature split). The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Excessive rise of high pressure of inverter compressor – indoor-unit (R134a stage) inverter PCB error, displayed with prefix "bc" (High Temperature split).
Part involved: indoor R134a inverter compressor / inverter PCB.
When it shows: Excessive rise of high pressure, causing compressor OFF.
Likely causes:
- Excessive rise of high pressure, causing compressor OFF.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: no.
Manual reset: Service-engineer repair and restart required (LG: resumed only after certificated professional's check).
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. This is an 'Error'-class fault: LG says the system can only be resumed after a qualified professional has checked it, so do not keep trying to restart it.
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 120 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026