LG Heat Pump Error Code 45

Error code 45 on an LG heat pump indicates that the outdoor unit pipe sensor on the left side has been detected with an open or short circuit fault. The control board cannot read a valid resistance signal from this thermistor, so it shuts down operation to protect the system. The fault points to either a wiring or connector issue, a failed sensor, or in rare cases, a faulty PCB input circuit.

A power reset may temporarily clear the error display, but the code will return immediately if the underlying sensor fault is still present. Because the PCB actively monitors the sensor signal during operation, a failed or disconnected thermistor will trigger the fault again as soon as the unit powers back up. The sensor connection and sensor condition must be physically corrected before the error will stay cleared.

If the fix is simply reseating a loose connector, you may incur only a diagnostic service call fee, typically in the range of $75 to $150 depending on your area. Replacing the outdoor pipe thermistor sensor is a relatively low-cost repair, with parts generally ranging from $20 to $60 and total repair costs including labor often falling between $100 and $250. If the outdoor unit PCB is the root cause, board replacement is significantly more expensive, often ranging from $300 to $600 or more with labor.

A knowledgeable DIYer can inspect the sensor connector at the outdoor PCB for loose or corroded pins and reseat it if needed, which sometimes clears the fault. However, testing thermistor resistance requires a multimeter and familiarity with reading sensor resistance curves, and working inside an outdoor unit involves refrigerant-side components that should be handled carefully. If the sensor or PCB needs replacement, a qualified HVAC technician is recommended.

In most cases the heat pump will not operate normally while error code 45 is active, as the system shuts down to protect the compressor and refrigerant circuit from running without accurate pipe temperature data. Attempting to bypass or ignore the fault is not recommended, since the pipe sensor data is used to manage defrost cycles and refrigerant flow control. Continued operation without a functioning sensor risks compressor damage.