LG Heat Pump Error Code E323

E323 indicates a fault with the SUMP TEMP FIXED 2 sensor in the outdoor unit. The control board has detected that the sensor's voltage signal is outside the valid range, either above 4.95V (indicating below -30°C) or below 0.5V (indicating above 151°C). This fault is only triggered when the outdoor temperature is above -10°C, so the system knows these readings are implausible. It points to an open or short circuit in the sensor or its wiring.

It is not advisable to continue operating the heat pump with E323 active. The sump temperature sensor helps protect the compressor by monitoring critical temperature conditions in the outdoor unit. Running without a reliable sensor reading could allow the system to operate outside safe parameters, potentially causing compressor damage or refrigerant system issues.

Repair costs vary depending on the cause. If only a connector needs cleaning or reseating, a service call fee of roughly $75 to $150 may cover it. Sensor replacement typically adds $30 to $100 in parts plus labor. If the control board requires replacement, total costs can range from $300 to $700 or more depending on the model and labor rates in your area.

A knowledgeable DIYer can inspect the sensor wiring and connectors for visible damage, corrosion, or loose connections, and even test the sensor's resistance with a multimeter. However, if the sensor itself needs replacement or the control board is involved, working inside an outdoor heat pump unit involves refrigerant system components and high voltage, so professional service is strongly recommended for those repairs.

A power cycle or reset may temporarily clear the error display, but E323 will return as soon as the control board re-evaluates the sensor signal and finds it still out of range. The underlying fault, whether a failed sensor, damaged wiring, or bad connection, must be physically diagnosed and corrected before the error will stay cleared.