LG Heat Pump Error Code CH18

CH18 on an LG heat pump signals a problem with the water-outlet temperature sensor. This sensor monitors the temperature of water exiting the heat exchanger and reports it to the main control board. When the signal is absent or out of range, the unit logs CH18 and may stop operating to protect internal components. The fault is confirmed by checking the sensor's resistance (5k ohm at 25 degrees Celsius unplugged) or its signal voltage (2.5Vdc at 25 degrees Celsius when connected).

It is not advisable to continue operating the unit while CH18 is active. The water-outlet sensor provides critical temperature feedback that the control board uses to protect the heat exchanger and refrigerant circuit. Running without accurate outlet temperature data can lead to overheating, freezing conditions, or accelerated wear on system components. Address the fault before resuming normal operation.

A power reset may temporarily clear the CH18 code, but if the underlying sensor fault is still present, the error will return once the unit runs through its startup diagnostics. Resetting without repairing the root cause does not fix the problem and can mask an ongoing issue. Use the reset only after you have confirmed the connector is secure and the sensor reads within spec, to verify the repair was successful.

A homeowner comfortable with basic electrical checks can start by inspecting the sensor connector at the PCB for looseness or corrosion and reseating it, which sometimes clears the fault. However, measuring resistance and voltage accurately requires a multimeter and some familiarity with reading wiring diagrams. If the sensor itself needs replacement or the PCB is suspect, a qualified technician is recommended to ensure safe handling of the refrigerant circuit and electrical components.

If the fix is simply reseating a loose connector, there may be no parts cost at all, only a service call fee which typically ranges from $75 to $150 depending on your area. Replacing the water-outlet sensor itself generally costs between $30 and $100 for the part, plus labor. If the PCB input circuit is damaged and the board requires replacement, total repair costs can range from $300 to $700 or more depending on the specific model and labor rates.