Microwave runs but does not heat; F4 appears on the display.

Critical safety warning: The inverter and high-voltage circuit store lethal voltages. Do not attempt to service the inverter, capacitor, or magnetron unless you are a qualified appliance technician with proper tools and training.

• Basic checks only: Unplug the microwave. Inspect the power cord and outlet for damage. Verify that the unit is on a dedicated circuit and not sharing power with high-load appliances.
• Reset power: Leave the unit unplugged for 10–15 minutes to allow internal electronics to discharge and reset. Plug back in and test.
• Observe operation: If the turntable and light work but food does not heat and F4 appears, the fault is likely in the inverter or magnetron circuit.
• Do not bypass safety devices: Never attempt to bypass door switches, thermostats, or fuses to "test" heating. This is extremely dangerous.
• Professional service recommended: Replacement of the inverter module or magnetron requires specialized procedures and leak testing. Contact a Miele-authorized service center.