LG Air Conditioner
LG AC CH21 error
Inverter board / power module protection
Try a reset once. If it comes back, a trained technician should repair it.
Also shown as: 21
What it means
The inverter drive (power module, DC voltage or heat sink) detected a fault and stopped the compressor.
Common causes
- Voltage spike or unstable supply
- Outdoor board overheating (poor air flow, very hot day)
- Failed power module or board parts
- Compressor wiring problem
Try this at home first
Tick each step as you go
When to call a technician
This needs a trained inverter technician. Users must never open boards or modules.
Safety first
Always switch off at the wall socket or MCB before touching any part. Do not open the outdoor unit, control boards or gas pipes yourself — they carry high voltage and pressure.
Frequently asked questions
What does CH21 mean on a LG Air Conditioner?
Inverter board / power module protection. The inverter drive (power module, DC voltage or heat sink) detected a fault and stopped the compressor.
Can I fix LG Air Conditioner error CH21 myself?
You can try a reset first: Switch off at the MCB for 10–15 minutes. If the code returns, call a technician.
Is it safe to keep using the Air Conditioner with CH21?
Avoid repeated restarts; running with this fault can cause more damage.
Other LG AC codes
Sources
We write every explanation in our own words from these references.
Last checked: 2026-10-20