LG Air Conditioner Error Code 124

Error code 124 indicates that the temperature sensor on the rear-side heat exchanger (B) of the sub1 outdoor unit has been detected as either open or short circuited. The system monitors this thermistor's resistance continuously, and when the value falls outside the acceptable range, the code is triggered. The unit will not operate normally until the fault is resolved. Diagnosis follows the CH45 procedure outlined for this fault type.

No, you should not attempt to bypass or override the error to continue running the unit. The rear heat exchanger sensor protects the system by monitoring coil temperatures, and operating without valid sensor data can lead to compressor damage or unsafe operating pressures. Leave the unit off until the fault has been properly diagnosed and repaired.

Resetting the unit by cycling power may temporarily clear the code and allow the system to restart, but if the underlying sensor or wiring fault is still present, the error will return. A reset does not repair a failed thermistor or damaged harness. The fault must be properly diagnosed and repaired to achieve a lasting resolution.

Some basic checks, such as inspecting the sensor wiring connector for looseness or visible corrosion, can be done by a knowledgeable homeowner with the unit powered off. However, accurately diagnosing the fault requires measuring thermistor resistance with a multimeter and comparing readings against a reference curve, which requires technical knowledge and proper tools. Replacing the sensor or control board involves working inside the outdoor unit and should be done by a qualified technician.

If the repair requires only a new thermistor sensor, parts costs are typically in the range of $15 to $60 depending on the specific model, with labor costs adding $75 to $200 depending on your location and the technician's rates. If the control board is the root cause, the total repair cost including parts and labor can range from $250 to $600 or more. A proper diagnosis following the CH45 procedure is needed before any cost estimate can be confirmed.