Microwave runs but does not heat; E03 appears on the display after a few seconds.
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Possible Causes
How to Fix / Troubleshooting
Critical safety warning: The high-voltage section (magnetron, transformer, capacitor, diode) can store lethal voltage even when unplugged. Do not attempt HV repairs unless you are a trained appliance technician.
- Step 1 – Basic checks: Confirm the unit has correct power (no dimming lights, no tripped breaker). Try different cook settings and verify the turntable and interior light operate.
- Step 2 – Rule out user issues: Test with a microwave-safe cup of water for 1–2 minutes. If the water remains cold and E03 appears, heating components are likely faulty.
- Step 3 – Visual inspection (qualified persons only): With power disconnected and capacitor safely discharged, inspect the magnetron for burn marks, cracks, or arcing. Check the HV diode and capacitor for bulging or damage.
- Step 4 – Component testing: Use a multimeter to test the high-voltage diode and transformer windings for continuity per Thermador service specs. Replace any component that tests open/shorted.
- Step 5 – Replace magnetron if needed: If the magnetron is open, shorted to ground, or visibly damaged, replace it with the exact Thermador-approved magnetron model.
Recommendation: Due to the danger and complexity, most homeowners should contact a Thermador-authorized service provider for E03 faults.