Bosch Microwave Error Code F-4

F-4 indicates a problem with the humidity sensor used during automatic sensor cooking modes. Specifically, the sensor's self-heating warm-up phase is taking longer than 64 seconds, or the zero-balancing voltage is not reaching the required 2.5-volt level. This prevents the sensor from establishing a reliable baseline before cooking begins. The code can only be cleared by pressing the CLEAR key.

Standard microwave heating functions are separate from the humidity sensor system, so basic manual cooking may still work. However, any cooking mode that relies on the humidity sensor will not function correctly while this fault is active. It is best to resolve the error before relying on sensor cooking modes to avoid improperly cooked food.

If the fault is caused by environmental conditions like moisture or temperature, there is no repair cost involved. If the humidity sensor itself needs to be replaced, parts and labor costs typically range from around $100 to $250 depending on the specific model and local labor rates. A wiring harness repair may fall at the lower end of that range if no new parts are required.

In many cases, yes. Start by pressing CLEAR, then make sure the oven has been plugged in for at least 5 minutes, that the room temperature is below 95 degrees Fahrenheit, and that both the oven interior and the outside of your cooking dish are completely dry. If the error returns after correcting these conditions, the humidity sensor or its wiring may need professional inspection and possible replacement.

The F-4 error can only be cleared using the CLEAR key on the control panel. Simply unplugging and replugging the unit may not permanently resolve the issue if the underlying cause, such as a wet oven interior or a failed sensor, has not been addressed. After clearing the code, confirm that all environmental conditions are correct before attempting sensor cooking again.