LG Heat Pump Error Code E422

E422 indicates a fault with the SUMP TEMP FIXED 2 sensor in the outdoor unit. The control board has detected a sensor voltage reading either above 4.95V (indicating an open circuit, interpreted as below -30°C) or below 0.5V (indicating a short circuit, interpreted as above 151°C). This error is only active when outdoor temperatures are above -10°C. It typically points to a failed thermistor, damaged wiring, or a loose connector.

It is not recommended to continue running the heat pump while E422 is active. The sump temperature sensor provides critical data that helps protect the compressor during low-ambient operation. Operating without a functional sensor could allow conditions that damage the compressor or other components. The unit should be inspected and repaired before returning to regular service.

A power reset may temporarily clear the E422 error from the display, but if the underlying sensor or wiring fault is still present, the error will return once the unit attempts to read the sensor again. Resetting the unit does not repair the hardware fault. A proper repair of the sensor, wiring, or control board is required to resolve the error permanently.

Some basic checks, such as inspecting the outdoor unit wiring for visible damage or reseating a loose connector, can be done by a knowledgeable homeowner. However, properly diagnosing this error requires measuring thermistor resistance and checking circuit voltages, which calls for a multimeter and familiarity with heat pump components. Replacing the sensor or control board should be performed by a qualified HVAC technician.

Repair costs will vary depending on the root cause. If only the thermistor sensor needs replacement, parts and labor costs typically fall in the range of $100 to $300. If the wiring harness needs repair or replacement, costs may be similar. A faulty outdoor control board is the most expensive possibility, with parts and labor potentially ranging from $400 to $900 or more depending on the model and technician rates in your area.