Microwave shows E020 and makes an unusual humming or buzzing noise without heating.

Critical safety warning: High-voltage components can be lethal. Do not attempt to service the HV circuit unless you are trained and can safely discharge the capacitor.

User-level checks:

• Inspect the interior for burn marks, especially near the waveguide cover (mica or plastic panel on the side or top).
• If the waveguide cover is burnt or has holes, stop using the microwave until it is replaced.

Technician-level checks:

• Remove the cabinet and inspect the HV capacitor and diode for signs of overheating.
• Discharge the capacitor safely, then test the capacitor and diode with appropriate equipment.
• Inspect the magnetron for internal shorts or visible damage.

Replace any shorted HV components and the waveguide cover if damaged. Because of the risks, this repair is best left to a Neff-authorized technician.