LG Heat Pump Error Code CH21

CH21 indicates a DC Peak fault caused by an instantaneous overcurrent detected in the U, V, or W output phase of the inverter's IPM (Intelligent Power Module). The unit shuts down immediately to protect the IPM from damage. The fault can stem from wiring problems, compressor faults, supply voltage issues, or a failing DC link capacitor. A qualified technician should diagnose the root cause before restarting the system.

No. The CH21 fault causes the unit to shut down specifically because continuing to operate with an overcurrent condition risks destroying the IPM and potentially damaging connected compressor windings. Operating the unit in a fault state could escalate a relatively inexpensive repair into a full compressor or inverter board replacement. Leave the unit off until the underlying cause is identified and corrected.

A power reset may temporarily clear the fault display, but if the underlying problem persists, the CH21 code will return, often immediately upon the next compressor startup attempt. Resetting without diagnosis does not fix the fault and can cause additional stress on the IPM each time the compressor tries to start against a fault condition. A proper repair requires identifying and correcting the root cause, whether that is a wiring issue, voltage problem, compressor fault, or a failed component.

Some preliminary checks, such as visually inspecting phase wire connections at the compressor for looseness or corrosion, can be performed by a knowledgeable DIYer. However, properly diagnosing this fault requires measuring live supply voltage, testing compressor winding resistance and insulation, and evaluating the DC link capacitor and IPM, all of which involve dangerous voltages. Most of the required diagnostic and repair work should be performed by a licensed HVAC or refrigeration technician.

Repair costs vary widely depending on the root cause. If the fix is simply reseating a loose wire connection, the cost may only be a service call fee, typically in the range of $80 to $200. Replacing a DC link capacitor or IPM module can run $300 to $700 or more including parts and labor. A failed compressor is the most expensive outcome, with replacement costs ranging from $1,000 to $2,500 or higher depending on the unit size and refrigerant type.