Microwave does not heat; display shows F3 shortly after starting a program.

Critical safety warning: High-voltage components inside a microwave (magnetron, capacitor, transformer) can cause severe injury or death. Do not attempt internal high-voltage repairs unless you are trained and equipped. When in doubt, contact a Miele-authorized technician.

• Check airflow: Ensure the rear and side vents are not blocked by cabinets or objects. Clean any dust buildup from intake and exhaust grilles.
• Listen for cooling fan: Start a short program and listen for the internal cooling fan. If the fan is not running, stop the unit immediately and unplug it. A failed fan can cause magnetron overheating and F3 errors.
• Inspect thermal cut-out (advanced): With power disconnected and cover removed, locate the magnetron thermal cut-out (small disc thermostat attached to the magnetron or waveguide). Check for loose wires or burned connectors.
• Test continuity: Using a multimeter, test the thermal cut-out for continuity. An open reading when the unit is cool indicates a failed cut-out that must be replaced.
• Replace faulty components: Replace the magnetron thermal cut-out or cooling fan motor if defective. If these parts are good, the magnetron or control board may be at fault and should be evaluated by a professional.