LG Microwave Error Code F-4

The F-4 code indicates a problem with the humidity sensor during a sensor cook operation. It means either the sensor's self-heating cycle exceeded 64 seconds or the zero balancing voltage in the sensor circuit did not rise to the required 2.5V. The microwave cannot complete sensor-based cooking until the fault is resolved. The humidity sensor or the PC board is typically responsible.

Unplugging the microwave and restoring power may temporarily clear the F-4 display, but the code will return as soon as a sensor cook cycle is initiated if the underlying hardware fault is not corrected. A reset does not fix a failed humidity sensor or a faulty PC board. The error will persist until the defective component is replaced.

If only the humidity sensor requires replacement, parts and labor typically range from around $75 to $175 depending on the model and service rates in your area. If the PC board also needs replacement, total repair costs can range from $150 to $350 or more. For older units, it is worth comparing repair costs against the price of a replacement microwave before proceeding.

Replacing the humidity sensor is the recommended first step and is a repair that a technically comfortable DIYer can attempt after unplugging the unit. If the error persists after a new sensor is installed, the PC board requires replacement, which is a more involved repair. Always disconnect power before opening the microwave cabinet, and be aware that the capacitor inside can hold a dangerous charge even after unplugging.

The microwave's sensor cook functions will not operate reliably with an F-4 fault present. Manual time cooking may still function, but sensor-based cooking modes should be avoided until the fault is repaired. There is no immediate safety hazard from the error itself, but operating the unit with a known component fault is not recommended.