Thermador Microwave E17 Error: Speed Oven Preheat Failed
What Does Thermador Microwave Error Code E17 Mean? The Thermador microwave E17 error code means the speed oven cavity did not reach the target temperature within the allowed preheat time. E17 applies exclusively to Thermador speed oven models — specifically the MCES, MCEW, MCBS, and MCBSL series — that combine a microwave magnetron with a […]
Quick Assessment
Answer to continue safely
Is it safe to keep using?
Maybe. Basic microwave-only programs may continue to operate normally while E17 is present, because the microwave circuit and the convection circuit are independent. However, all convection, speed cook, and combination programs must not be used until E17 is diagnosed and resolved. Schedule service promptly.
Can I reset the code?
Yes. A breaker reset may clear E17 if the fault was caused by a transient sensor reading or a firmware glitch during preheat. If the convection element or its relay has genuinely failed, E17 returns on the next convection preheat attempt regardless of resets.
When to stop immediately?
Stop if you notice: E17 appears on every convection or speed cook preheat attempt after a full reset, Cavity interior feels no warmer than ambient temperature after a preheat cycle.
Symptoms You May Notice
Speed oven displays E17 during preheat and cancels the selected program
The unit begins preheating for a convection or combination cook program, runs the heating element for the full preheat period, then displays E17 and cancels because the target temperature was not confirmed by the cavity sensor.
Convection or combination cooking modes fail while basic microwave programs run normally
Simple microwave-only programs complete without error, but any mode that requires the convection element -- speed cook, combination cook, or convection bake on Thermador MCES and MCEW speed ovens -- triggers E17 during preheat.
Speed oven cavity feels only slightly warm after a full preheat attempt
When E17 appears, the cavity interior is noticeably cooler than expected for the selected temperature, confirming the heating element or its circuit did not reach the required level during the preheat window.
Possible Causes
Failed convection heating element
The convection element in the speed oven cavity has burned out or gone partially open, producing insufficient heat to bring the cavity to temperature within the preheat time limit. This is the most common hardware cause of E17 on Thermador MCES, MCEW, MCBS, and MCBSL speed ovens.
Requires ProfessionalFaulty cavity temperature sensor
The NTC thermistor monitoring cavity temperature is reading lower than actual temperature, causing the control board to conclude the cavity has not reached target even when the element is generating adequate heat.
Requires ProfessionalFaulty convection element relay or control board output
The relay that switches power to the convection element has failed open, preventing current from reaching the element regardless of control board commands. The element itself may be intact.
Requires ProfessionalSafe Checks You Can Do
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1
Reset the speed oven at the circuit breaker
Switch the dedicated circuit breaker for the speed oven off for five minutes and restore power. Attempt a convection preheat program at a moderate temperature -- 325 F is a good test point -- and observe whether E17 appears. A transient sensor or firmware fault may clear with a cold restart.
E17 on Thermador MCES and MCEW speed ovens is distinct from Er4 (extreme overheat safety shutoff). Er4 indicates the cavity exceeded the safe temperature ceiling; E17 means the cavity could not reach the target temperature at all. If the display previously showed <a href="/error-codes/microwave/microwave-er4/">Er4</a>, do not assume E17 is the same type of fault.
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2
Test microwave-only functions to isolate the fault
While waiting for service, test whether basic microwave-only programs -- timed cooking at a fixed power level -- complete normally. If microwave functions work and only convection or speed cook modes trigger E17, the convection heating circuit rather than the microwave circuit is at fault. Record which programs succeed and which fail for the technician.
E17 applies only to Thermador speed oven models (MCES, MCEW, MCBS, MCBSL series) that include a convection heating element. It does not appear on MBES microwave-only built-ins, which have no convection element to preheat.
When to Call a Professional
Contact a qualified technician if:
- Convection element shows open circuit resistance on a multimeter, confirming element failure
- E17 reproduces on every convection preheat after a five-minute reset
- Cavity temperature sensor reads outside the expected resistance range at room temperature, pointing to a sensor fault rather than element failure
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