LG Heat Pump Error Code E303

E303 indicates a condenser outlet main temperature sensor fault, specifically an OPEN or SHORT condition detected by the control board. The sensor, which monitors refrigerant temperature at the condenser coil outlet, is sending a signal outside the valid resistance range. This prevents the unit from operating safely until the sensor circuit is restored to normal function.

It is not advisable to continue operating the unit while the E303 error is active. The condenser outlet temperature sensor provides data the control board uses to protect the compressor and manage refrigerant flow. Operating without a valid sensor reading can lead to undetected high temperatures or refrigerant conditions that may cause compressor damage or other component failures.

A power reset may temporarily clear the error code, but if the underlying sensor fault, such as a failed thermistor or broken wire, is still present, E303 will return once the system reinitializes and rechecks the sensor circuit. A reset is a reasonable first step to rule out a transient fault, but persistent reappearance of the code means the sensor, wiring, or connector requires physical inspection and likely repair.

Some basic steps are accessible to a knowledgeable DIYer, such as checking whether the sensor connector has come loose from the PCB and reseating it securely. However, measuring thermistor resistance accurately requires a multimeter and familiarity with the expected resistance values for the sensor. If the sensor or wiring needs replacement, a qualified HVAC technician is recommended, especially since heat pump refrigerant systems require licensed handling.

If the fix is simply reseating a loose connector, there may be no parts cost, only a service call fee which typically ranges from $75 to $150. If the thermistor sensor itself needs replacement, parts generally range from $20 to $80 depending on the specific model, plus labor. A full diagnostic service call including sensor replacement could range from $100 to $300 in total.