F40
Miele
Mains Frequency / Voltage Detection Fault
Microwave shows F40 and will not operate; often related to mains frequency or voltage.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Incorrect mains frequency (e.g., 60 Hz unit on 50 Hz supply), Unstable or out-of-range mains voltage, Faulty mains sensing circuit on control board, Installation on incompatible power system
How to Fix / Troubleshooting
Safety first: Switch off the circuit breaker before inspecting electrical connections.
- Verify supply: Confirm that the microwave model is rated for your local voltage and frequency (e.g., 230 V / 50 Hz). This information is on the rating plate.
- Check circuit: Ensure the unit is on a dedicated circuit with proper grounding. Avoid long extension cords.
- Measure voltage (qualified persons only): Use a multimeter to verify that the supply voltage is within the range specified by Miele.
- Power reset: Turn off the breaker for 10 minutes, then restore power and test.
- Control board: If supply is correct and F40 persists, the mains sensing circuit on the control board may be defective and should be replaced by a Miele technician.
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Repair Difficulty
Hard
4/5
Required Part
Main Control Module (Mains Sensing Circuit)
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