LG Refrigerator Error Code F3 F4

The F3 F4 error code on an LG refrigerator indicates a fault in the defrost circuit, specifically that the defrost heater and the thermal fuse (temperature fuse) have both lost continuity, meaning the circuit is open and current cannot flow. The refrigerator's control board monitors the defrost system and only triggers this code after detecting the fault condition for a minimum of four hours, which helps prevent false alarms from brief or transient anomalies. When both components show as cut or disconnected, the refrigerator cannot complete its automatic defrost cycles, leading to progressive frost and ice accumulation on the evaporator coil.

The defrost heater is a resistive heating element located near the evaporator coil in the freezer compartment. Its job is to melt frost buildup off the coil at regular intervals. The thermal fuse is a one-time safety device wired in series with the heater. If the defrost system overheats, the thermal fuse opens permanently to prevent damage, which also cuts power to the heater. When both components read as open, the root cause is often a failed thermal fuse that tripped due to a malfunctioning defrost thermostat, a blocked drain, or a heater that ran too long.

Diagnosing this fault requires checking continuity on both the defrost heater and the thermal fuse using a multimeter. A properly functioning defrost heater will show measurable resistance across its terminals, while a good thermal fuse will show near-zero resistance (continuity). Either component reading as open circuit confirms it has failed and requires replacement before the defrost system can operate normally again.