Thermador Microwave E1003 Error: Inverter Communication Fault
What Does Thermador Microwave Error Code E1003 Mean? The Thermador microwave E1003 error code indicates the main control board has lost the feedback signal from the inverter board that powers the magnetron. Thermador Professional and Masterpiece built-in microwaves in the MBES, MBESL, and MCES series use an inverter-based power system shared with Bosch HMB and […]
Quick Assessment
Answer to continue safely
Is it safe to keep using?
No. The microwave must not be used while E1003 is active. The inverter circuit that powers the magnetron is operating outside verified parameters. Using the unit risks uncontrolled magnetron behavior and potential damage to the appliance.
Can I reset the code?
Yes. A five-minute breaker reset may clear E1003 if the fault was caused by a transient power event or a momentary communication glitch. If the inverter board has genuinely failed, E1003 returns on the next cook attempt regardless of how many resets are performed.
When to stop immediately?
Stop if you notice: E1003 returns immediately on every cook attempt after a full five-minute reset, A burning smell or acrid odor comes from the microwave cabinet during or after E1003.
Symptoms You May Notice
Microwave runs for a few seconds then goes silent with E1003 on display
The unit energizes, the turntable begins to rotate, but within 3 to 10 seconds the magnetron cuts out and the display locks on E1003 -- the inverter board failed to send a feedback pulse back to the control.
No heat produced even at maximum power level
The microwave appears to run -- the light, turntable, and fan operate normally -- but food remains cold because the magnetron is not receiving power from the inverter.
E1003 appears immediately when a cook program is started
On Thermador MBES and MCES models with a fully failed inverter board, the error triggers before the first magnetron pulse rather than after a brief heating attempt.
Possible Causes
Failed inverter board
The inverter board that converts line voltage into the high-frequency power the magnetron requires has failed. This is the most common hardware cause of E1003 on BSH-platform Thermador MBES, MBESL, and MCES microwaves.
Requires ProfessionalBroken feedback wiring between inverter and control board
The signal wire that carries inverter status back to the main control board has broken or pulled loose from its connector. The inverter may be functioning but the control board receives no confirmation signal.
Requires ProfessionalFailed main control board unable to interpret inverter signal
In cases where E1003 progresses to E1006 or E1007, the main control board itself has failed and can no longer process the feedback signal even when the inverter is operating correctly.
Requires ProfessionalSafe Checks You Can Do
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1
Reset the microwave at the circuit breaker for five minutes
Switch the dedicated microwave circuit breaker off and leave it off for five full minutes. This discharges capacitors on the BSH inverter and control boards and allows a clean cold restart. Restore power and attempt a one-minute manual cook program to see whether E1003 returns.
A five-minute breaker reset is more effective on BSH-platform inverter microwaves than a 30-second reset. If E1003 does not return after the reset, monitor the unit over several days -- transient inverter communication faults can recur as the inverter board ages.
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2
Check for a recent power surge or outage
Note whether E1003 appeared after a thunderstorm, utility event, or grid disturbance. The high-voltage inverter circuit is sensitive to electrical transients. If a surge preceded the fault, the inverter board may have sustained damage that will not clear with a reset.
Standard plug-in surge protectors do not fully shield a built-in microwave from a direct utility surge because the appliance is wired directly to the panel. A whole-home surge protector is the only meaningful protection for hardwired appliances.
When to Call a Professional
Contact a qualified technician if:
- E1003 reproduces on every cook program after a five-minute breaker reset
- No magnetron activity detected even at maximum power -- fan and turntable run but no heat is produced
- E1003 progresses to E1006 or E1007, indicating a cascading BSH inverter fault chain requiring board-level diagnosis
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