LG Oven Error Code F-4

F-4 means the lower oven thermistor has been detected as an open circuit for more than one minute after a cooking cycle starts. The thermistor is the temperature sensor that tells the control board how hot the oven cavity is. Without a valid reading, the oven cannot regulate heat safely and shuts down. The fault points to the thermistor, its wiring, or the CN05 connector.

No. The oven disables the cooking function precisely because it cannot safely monitor cavity temperature without the thermistor signal. Attempting to bypass or ignore this fault could result in uncontrolled overheating. The oven should not be used until the sensor circuit is repaired and tested.

If only the thermistor needs replacement, parts and labor typically range from around $100 to $250 depending on your location and service provider. If the wiring harness is damaged, costs can rise into the $150 to $350 range. A control board replacement, if required, is generally the most expensive outcome, often falling between $200 and $450 or more including labor.

Technicians and experienced DIYers can diagnose this fault using test mode 4 to check the sensor reading, then measuring resistance at connector CN05 with a multimeter. The expected room-temperature resistance is approximately 1.09 kΩ. If the thermistor is confirmed failed, replacing it is a relatively straightforward repair, but all work should be done with the oven fully powered off and unplugged.

A power reset may temporarily clear the fault code, but F-4 will return as soon as the next cook cycle starts if the underlying problem is not fixed. The control board checks the thermistor signal within the first minute of operation, so any open circuit condition will trigger the code again quickly. A reset is only useful as a diagnostic step, not a repair.