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

Critical Safety Warning: The high-voltage section of a microwave (transformer, capacitor, diode, magnetron) can be lethal. Do not attempt internal repairs unless you are a qualified technician with proper tools and training.

User-level steps:

• Unplug the microwave and leave it unplugged.
• Verify that the unit is not in demo mode (refer to the user manual). Demo mode can simulate operation without heating.
• Try heating a cup of water for 1–2 minutes. If the turntable rotates and light comes on but the water stays cold and E03 appears, the issue is internal to the high-voltage system.

Technician-level steps:

• Discharge the high-voltage capacitor safely using a resistor and insulated tools.
• Test the high-voltage diode for one-way continuity; replace if shorted or open.
• Check the HV capacitor for shorts or open condition with a capacitance meter.
• Inspect and test the magnetron for continuity and shorts to ground.
• Measure primary and secondary windings of the HV transformer for proper resistance.

Replace any failed component with a Summit-compatible high-voltage part set. Due to the danger and complexity, most homeowners should have a professional perform this repair.