LG Heat Pump Error Code 21

Error code 21, displayed as CH21 on LG heat pumps, indicates a DC peak fault involving the Intelligent Power Module (IPM). The fault is triggered by an over-current condition, an over-temperature condition in the IPM, or a compressor malfunction that has occurred three times within one hour. The unit locks out to protect internal components from further damage.

No. The unit has already detected a serious electrical fault three times within one hour and has shut down for protection. Attempting to force the system to run while this fault is active risks further damage to the IPM, the compressor, or the control board. Keep the unit off until the fault is properly diagnosed and resolved.

Repair costs vary widely depending on the root cause. A simple terminal cleaning or reseating of connections may only involve a service call fee, typically in the range of $80 to $150. Compressor replacement is the most expensive outcome, often ranging from $800 to $2,000 or more depending on the unit size and labor rates. IPM board replacement generally falls somewhere in between, often in the $300 to $700 range for parts and labor.

Some basic checks, such as inspecting IPM terminal connections for looseness or moisture, can be performed by a knowledgeable DIYer. However, testing compressor windings, evaluating the IPM for internal faults, and working around high-voltage DC bus circuitry involves serious electrical hazards. Most repairs that go beyond visual inspection should be handled by a qualified technician.

A power reset may temporarily clear the fault and allow the unit to restart, but if the underlying problem is still present, the unit will trip again and re-display CH21. Because the code requires three fault events within one hour, a reset without fixing the root cause simply delays the lockout. The fault must be diagnosed and corrected to achieve a lasting resolution.