LG Heat Pump Error Code E104

E104 indicates that the evaporator outlet temperature sensor on the indoor unit has an open or short circuit fault. The sensor is a thermistor that monitors refrigerant temperature at the exit of the indoor coil. When the PCB detects a resistance reading outside the valid range, it triggers this code and stops normal operation. The sensor, its wiring, or the connector are typically responsible.

No. The unit will typically prevent normal operation when E104 is active because it cannot reliably monitor the evaporator outlet temperature. Attempting to bypass or ignore the fault could result in uncontrolled refrigerant behavior, coil icing, or compressor damage. The system should remain off until the sensor fault is resolved.

A power reset may temporarily clear the displayed code, but E104 will return as soon as the indoor PCB polls the sensor again and detects the out-of-range resistance. Because the fault reflects an actual electrical problem with the sensor circuit, resetting the unit does not address the underlying issue. Proper diagnosis and repair of the sensor or wiring are required for a lasting fix.

A knowledgeable DIYer can perform the initial resistance check by disconnecting the sensor connector from the indoor PCB and measuring across the two terminals with a multimeter. If the connector was simply loose, reseating it may resolve the fault. However, replacing the thermistor or diagnosing PCB-level issues generally requires familiarity with HVAC electrical components, and refrigerant-related work requires a certified technician.

Repair costs depend on the root cause. A replacement NTC evaporator sensor typically costs between $15 and $60 for the part alone. With professional labor, the total repair including diagnosis and part replacement usually ranges from $100 to $300. If the indoor PCB is at fault, costs can increase significantly, often ranging from $250 to $600 or more depending on the board and labor rates in your area.