LG Heat Pump Error Code 42

Error code 42 on an LG heat pump means the low pressure sensor has been detected in an open or short circuit condition. The PCB is not receiving a valid signal from the sensor that monitors refrigerant pressure on the suction side of the system. As a protective measure, the unit typically shuts down to prevent compressor damage until the fault is resolved.

No, you should not attempt to force the unit to run while error code 42 is active. The low pressure sensor is a protective device, and operating the system without a valid pressure reading risks serious compressor damage. Leave the unit off and have the fault diagnosed before resuming normal operation.

Repair costs vary depending on what is causing the fault. If the fix is simply reseating a connector, you may only pay a diagnostic or service call fee, typically in the range of $75 to $150. Replacing the low pressure sensor itself generally costs between $100 and $300 including parts and labor. If the PCB requires replacement, costs can range from $300 to $700 or more depending on the specific model and labor rates in your area.

A knowledgeable homeowner can safely check whether the sensor connector at the PCB is fully seated and free of visible corrosion, which sometimes clears the fault. However, measuring sensor resistance or voltage and replacing refrigerant-circuit components typically requires the tools and training of a qualified HVAC technician. Working on refrigerant systems also requires proper certification in most regions.

A power reset may temporarily clear the error code, but if the underlying sensor fault still exists, the code will return once the unit attempts to operate. A reset alone does not repair an open or shorted sensor, a damaged wire, or a faulty connector. The root cause must be identified and corrected for the fault to clear permanently.