Display shows F4; interior light and controls may behave erratically, or unit may not start.

Safety: Disconnect power before removing switch housings or trim.

Steps:

• Check door operation: Open and close the door while observing the interior light and display. If the light flickers or does not respond, suspect the door switch.
• Inspect door gasket and alignment: Ensure the door closes fully and evenly. A misaligned door may not actuate the switch or magnet properly.
• Locate the switch: On many Miele models, the door switch is in the cabinet frame or integrated as a reed switch behind trim. Gently pry off the trim to access it.
• Test the switch: With a multimeter, check continuity while pressing the switch plunger or moving a magnet near a reed switch. Replace if readings are inconsistent.
• Check wiring: Inspect for broken or pinched wires near the hinge area where the harness flexes.

If the switch and wiring are intact but F4 persists, the input circuit on the main control board may be defective and requires professional service.