LG Heat Pump Error Code E108

E108 indicates a fault with auxiliary heater sensor 1, the thermistor that monitors the electric backup heating element in the unit. The control board has detected a signal from that sensor that is outside the acceptable range, which triggers the error to protect against unsafe heater operation. The fault could be in the sensor itself, its wiring, or the connector.

Operating the unit with an active E108 error is not recommended. The auxiliary heater sensor exists to monitor safe temperature conditions around the electric heating element, and without a reliable sensor signal, the control board cannot confirm the heater is operating within safe limits. Continued use could allow the auxiliary heater to operate in an unmonitored state, which presents a potential safety risk.

A power reset may temporarily clear the error code, but if the underlying fault in the sensor or wiring still exists, E108 will return once the system attempts to operate the auxiliary heater. A reset is a reasonable first step to rule out a transient signal issue, but a persistent or recurring E108 code requires hands-on diagnostic work to identify and correct the root cause.

Basic checks such as inspecting and reseating the sensor connector are within reach for a confident DIYer comfortable working with low-voltage wiring. However, the auxiliary heater circuit involves high-voltage electric heating elements, and testing or replacing components in that area should be handled by a qualified technician. Attempting repairs without proper knowledge of electrical safety around high-voltage components is not advisable.

Repair costs vary depending on the root cause. If the fix is simply reseating a connector or cleaning a corroded terminal, the cost may be limited to a service call fee, typically in the range of $75 to $150. Thermistor replacement is generally an inexpensive part but labor costs bring the total to roughly $150 to $300. A control board replacement, if needed, would be the most expensive outcome, potentially ranging from $400 to $700 or more depending on the model.