LG Air Conditioner Error Code E123

E123 means the indoor unit's heat exchanger outlet temperature sensor has detected an open or short circuit fault. The control board is not receiving a valid signal from the sensor, so the system shuts down to prevent unsafe operation. The sensor, its wiring, and the indoor PCB connection are the primary areas to inspect.

No. The E123 error causes the unit to shut down because the control board cannot monitor heat exchanger temperatures accurately. Attempting to bypass or ignore this error could allow the coil to freeze or the system to operate in an uncontrolled state, potentially causing further component damage. The unit should remain off until the sensor fault is resolved.

Repair costs vary depending on what component has failed. A replacement heat exchanger outlet temperature sensor is generally an inexpensive part, with the sensor itself typically ranging from $10 to $40. Labor charges for a technician to diagnose and replace the sensor can bring the total to roughly $75 to $200. If the indoor PCB is at fault, costs can range from $150 to $400 or more depending on the unit model.

Some basic checks, such as inspecting the sensor connector at the PCB for looseness or visible damage, can be done by a careful DIYer after powering down all units completely. However, properly testing NTC sensor resistance with a multimeter and replacing the sensor or PCB typically requires comfort with electronics and appliance disassembly. If you are not confident working inside the indoor unit, a qualified HVAC technician is recommended.

A power reset may temporarily clear the error code, but E123 will return if the underlying sensor fault is still present. Because the code is triggered by a measurable electrical fault (open or short circuit), it is not a soft error that resolves on its own. A proper repair of the sensor, wiring, or PCB is required for the error to stay cleared.