LG Refrigerator Error Code F3 F4

The F3 F4 code indicates that the defrost heater and the thermal fuse in the defrost circuit have both lost continuity, meaning the automatic defrost system cannot operate. LG refrigerators only display this code after the fault has been present for at least four hours, so it reflects a confirmed and persistent problem rather than a brief glitch. Without a working defrost system, frost will build up on the evaporator coil and eventually impair cooling performance.

Continued use is not recommended for extended periods. Without a functioning defrost cycle, ice accumulates on the evaporator coil and eventually blocks airflow, which prevents the refrigerator from maintaining safe food storage temperatures. Food safety can become a concern relatively quickly once cooling performance degrades significantly.

A power reset may temporarily clear the code from the display, but the underlying fault will remain and the code will return once the control board re-evaluates the defrost circuit, typically within four hours. The only way to permanently resolve F3 F4 is to repair or replace the failed defrost heater, thermal fuse, or any other faulty component in the defrost circuit.

A knowledgeable DIYer with a multimeter can diagnose this fault by testing continuity on the defrost heater and thermal fuse after accessing the evaporator panel in the freezer compartment. If either component tests as open circuit, replacing it is a straightforward parts swap. However, if the root cause is a failing defrost thermostat or a blocked drain, those issues must also be addressed or the new parts may fail again quickly.

Repair costs vary depending on which components need replacement and whether you hire a technician. A thermal fuse typically costs between $5 and $20 for the part, while a defrost heater assembly generally ranges from $20 to $60. Adding professional labor, total repair costs commonly fall between $100 and $250, though pricing varies by region and service provider.