LG Heat Pump Error Code E408

E408 indicates a fault with the discharge temperature sensor on fixed capacity compressor 1 in the outdoor unit. The control board has detected either an open circuit or a short circuit from this sensor, which prevents it from reading a valid compressor discharge temperature. The fault is only triggered when outdoor temperatures are above -10 degrees Celsius. The system shuts down to protect the compressor until the sensor issue is resolved.

No. The E408 fault causes the system to shut down specifically because the discharge temperature sensor is needed to protect the compressor from overheating. Attempting to bypass or ignore this fault and force the unit to operate could result in compressor damage, which is one of the most expensive repairs on a heat pump. The unit should remain off until the fault is diagnosed and corrected.

Repair costs depend on the root cause. If the sensor connector simply needs to be reseated, you may only pay a diagnostic service call fee, typically in the range of $75 to $150. Replacing the discharge temperature sensor itself generally costs between $100 and $300 including parts and labor. If the outdoor PCB has failed, costs can range from $400 to $900 or more depending on the unit model and labor rates in your area.

A homeowner can safely check whether the sensor connector has come loose at the outdoor unit PCB, which requires no special tools and sometimes resolves the error. However, measuring sensor resistance, inspecting the wiring harness, and replacing the thermistor or PCB are tasks best handled by a qualified HVAC technician with experience on LG heat pump systems. Refrigerant circuits and high-voltage components in the outdoor unit present safety risks to untrained individuals.

A power reset may temporarily clear the fault code, but the error will return as soon as the system attempts to operate if the underlying sensor problem has not been repaired. Since the PCB continuously monitors sensor resistance during operation, any open or short condition will trigger E408 again quickly. A reset alone is not a fix and should only be used after the sensor, wiring, and connector have been inspected and corrected.