LG Heat Pump Error Code P521

P521 indicates an outdoor unit Electronic Expansion Valve (EEV) open 3 self-diagnosis error. The system ran an internal test and determined that the EEV failed to respond correctly to a commanded open position. This points to a problem with the valve itself, its stepper motor coil, the connecting wiring, or the outdoor control board.

Running the system with a P521 error is not recommended. A malfunctioning EEV cannot properly regulate refrigerant flow, which can lead to compressor damage, reduced efficiency, or further system failures. The unit should be shut down until the fault is diagnosed and repaired.

Repair costs depend on the specific failed component. EEV coil replacement is generally less expensive, while a full valve body replacement or outdoor control board replacement will cost more. Total repair costs including labor typically range from a few hundred dollars to over a thousand dollars, depending on parts pricing and labor rates in your area.

Some basic checks, such as inspecting the EEV wiring harness and connector for loose pins or corrosion, can be done by a knowledgeable DIYer. However, testing coil resistance, diagnosing the control board, and replacing the EEV valve or refrigerant components require proper tools and, in the case of refrigerant handling, EPA certification. It is strongly recommended to have a qualified HVAC technician complete the repair.

A power reset may temporarily clear the error code, but if the underlying cause such as a failed coil, stuck valve, or damaged wiring is still present, the P521 code will return once the system runs its self-diagnosis again. A reset alone is not a repair and should not be relied on as a solution.