Thermador Microwave ER1 Error: Temperature Sensor Fault
Thermador microwave Er1 error indicates temperature sensor fault. Stop using the appliance and call a Thermador-certified technician immediately for diagnosis. What Does Thermador Microwave Error Code Er1 Mean? The Er1 error code on a Thermador Professional or Masterpiece built-in microwave or speed oven indicates a faulty temperature sensor. This code is shared across the BSH […]
Quick Assessment
Answer to continue safely
Is it safe to keep using?
Maybe. Limited manual timed programs may run while awaiting service. Do not use auto-cook or sensor-cook programs. Schedule service promptly because Er1 indicates the thermal protection circuit is compromised.
Can I reset the code?
Yes. A breaker reset may clear Er1 temporarily if the fault was a transient sensor glitch. Genuine sensor failure will cause Er1 to return on the next auto-cook program or within a few cycles.
When to stop immediately?
Stop if you notice: Er1 appears on every cycle including manual programs, Burning smell from the microwave cavity or vent.
Symptoms You May Notice
Automatic cooking programs refuse to start
Any program that uses the built-in sensor — auto-defrost, auto-reheat, or combination cooking on Thermador speed ovens — immediately displays Er1 and cancels.
Manual programs complete but the display briefly shows Er1 at startup
Basic timed cooking at a fixed power level runs to completion, but Er1 flashes for a moment at the beginning of each cycle before the timer counts down.
Microwave cavity temperature feels inconsistent between uses
The cavity is noticeably hotter or cooler than expected at the end of a program, suggesting the thermal protection circuit is not actively managing magnetron output.
Possible Causes
Failed NTC thermistor in the microwave cavity
The negative temperature coefficient resistor that senses cavity temperature has failed open or short, making its reading invalid to the control board.
Requires ProfessionalLoose or corroded sensor connector
The quick-disconnect connector between the temperature sensor and the main wiring harness has loosened from vibration or corroded from kitchen steam exposure.
Requires ProfessionalControl board unable to read sensor output
The analog-to-digital converter circuit on the control board that interprets the sensor signal has failed, even though the sensor itself is physically intact.
Requires ProfessionalSafe Checks You Can Do
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1
Power-cycle the unit at the breaker
Switch the circuit breaker off for five minutes and restore power. On Thermador BSH-platform microwaves, a cold restart reinitializes all sensor monitoring routines. If Er1 does not return during the next manual cooking program, the fault was transient.
Er1 caused by a momentary connector vibration event can clear with a reset and remain absent for weeks. Monitor closely — intermittent Er1 usually becomes permanent as the connector or sensor ages further.
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2
Limit use to manual timed programs
While waiting for service, use the microwave only with manual time-cook programs at fixed power levels. Do not use auto-cook, sensor-cook, or any combination oven program on Thermador MBES or MCES speed ovens that rely on temperature feedback.
The Er1 sensor fault removes the thermal protection circuit from active duty. Manual programs will still operate, but without sensor-based power modulation the microwave cannot protect against cavity overheating in auto programs.
When to Call a Professional
Contact a qualified technician if:
- NTC thermistor measures open circuit or shorted on a multimeter at room temperature
- Er1 persists after reset and appears during all cooking programs
- Sensor connector pins show visible corrosion or discoloration
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