LG Heat Pump Error Code Fx

The Fx error code indicates that both the EVAP IN and EVAP OUT temperature sensors on a specific indoor unit have simultaneously lost connection or broken away from their mounting positions. The "x" represents the address of the affected indoor unit in multi-zone systems. The system shuts down that unit to prevent unsafe evaporator operation without valid temperature data. Reconnecting or reseating the sensors is the first step toward resolving the fault.

The error prevents the affected indoor unit from operating without valid temperature sensor readings, which actually protects the system from potential damage such as evaporator freezing or refrigerant slugging. The fault itself is not a hazard to your home, but the indoor unit will not function until the sensors are restored. Other indoor units in a multi-zone system may continue to operate normally.

If the sensors simply need to be reseated with no parts required, a service call to diagnose and reseat the sensors typically ranges from around $75 to $200 depending on labor rates in your area. If one or both sensors need replacement, parts costs can add roughly $20 to $80 per sensor on top of labor. Complex wiring harness repairs may push the total higher.

If you are comfortable opening the indoor unit cabinet, you can inspect whether the two sensors have physically come loose from their mounting clips or wells and carefully reseat them. However, if the wiring is damaged or the sensors themselves need replacing, a qualified HVAC technician should perform that work. Reconnecting sensors incorrectly to the wrong positions can cause additional faults or equipment damage.

A simple power reset will not permanently clear the Fx fault if the sensors are still disconnected or unresponsive. The control board will detect the missing sensor signals again upon restart and repost the error. The fault will only clear reliably once both the EVAP IN and EVAP OUT sensors are properly reconnected and the board confirms valid readings from each.