Microwave runs but does not heat; display shows E03 after a few seconds.

Critical safety notice: High-voltage components inside a microwave (transformer, capacitor, diode, magnetron) can store and generate lethal voltages. Do not attempt to service these parts unless you are a trained appliance technician with proper tools and procedures for discharging the capacitor.

User-level checks:

• 1. Confirm symptom: Place a microwave-safe cup of water inside and run for 1–2 minutes. If the turntable rotates and the interior light is on but the water remains cold and E03 appears, the high-voltage system is likely at fault.
• 2. Check power supply: Verify the outlet voltage is correct and stable. Avoid using long or undersized extension cords.

Technician-level overview (for diagnosis only):

• 3. Inspect high-voltage components: With the unit unplugged and capacitor safely discharged, visually inspect the high-voltage transformer, capacitor, and diode for burn marks, bulging, or melted insulation.
• 4. Test components: Use appropriate test procedures and a high-voltage-rated meter to check the transformer windings, capacitor, and diode. Replace any component that tests out of specification.
• 5. Check magnetron continuity: Test the magnetron filament for continuity and check for shorts to ground. Replace the magnetron if defective.

Because of the risks involved, most users should contact an authorized Blomberg service center when E03 appears.