LG Heat Pump Error Code E427

E427 is a reverse phase detection error for the outdoor unit, indicating the control board has identified that the three-phase power supply is arriving in an incorrect sequence. Three-phase systems require power to arrive in a specific L1, L2, L3 order for motors and the compressor to rotate correctly. The unit shuts down as a protective measure to prevent mechanical damage from reverse rotation. A phase rotation meter and inspection of the power supply wiring are the first steps in diagnosing this error.

No, the system should not be operated while E427 is active. Running a compressor or fan motor in reverse due to incorrect phase sequence can cause rapid mechanical damage and may create additional electrical hazards. The outdoor unit's control board is designed to prevent operation under this condition, and you should leave the system off until the power supply issue is resolved.

If the fix is simply swapping two phase conductors at the wiring connection, you can expect to pay primarily for the electrician or technician's service call and labor, typically in the range of $75 to $200 depending on your location. If the outdoor unit control board has failed and needs replacement, parts and labor costs can range from $300 to $700 or more. Getting a diagnosis from a qualified technician first will help clarify which repair is needed before committing to parts costs.

Correcting a phase sequence issue involves working directly with three-phase high-voltage electrical wiring, which should only be performed by a licensed electrician or certified HVAC technician. If the cause is swapped wiring at the disconnect or terminal block, the fix is straightforward for a qualified professional. Do not attempt to swap power conductors without the proper training, tools, and safety equipment.

A power cycle reset may temporarily clear the fault display, but E427 will return immediately if the underlying phase sequence problem has not been corrected. In some cases where the fault was triggered by a momentary grid disturbance, the error may not return after a reset if power quality has been restored. However, you should always verify the phase sequence with a rotation meter before concluding the issue is resolved.