Thermador Microwave ER18 Error: General Technical Fault
Thermador microwave Er18 error indicates general technical fault. Review the diagnostic steps below before calling a technician for help. What Does Thermador Microwave Error Code Er18 Mean? The Er18 error code on a Thermador Professional or Masterpiece built-in microwave represents a general technical fault — the BSH-platform control board has detected an abnormal condition that […]
Quick Assessment
Answer to continue safely
Is it safe to keep using?
Maybe. If Er18 clears after a reset and does not return immediately, limited use is possible while you monitor. If Er18 appears on every startup or multiple consecutive uses, stop using the unit and schedule service.
Can I reset the code?
Yes. Er18 clears with a five-minute breaker reset in most cases. Recurring Er18 after reset indicates an underlying electronics or ventilation fault that needs professional diagnosis.
When to stop immediately?
Stop if you notice: Er18 appears on every startup after reset, Er18 combined with Er4 or any other concurrent fault code.
Symptoms You May Notice
Microwave displays Er18 at startup and will not begin any program
Immediately after power is restored, the unit shows Er18 and ignores all touchpad input.
Microwave completes a cycle but shows Er18 immediately after
The cooking program finishes, but as the unit returns to standby mode it displays Er18, indicating the fault occurred during or at the end of the cycle.
Er18 appears intermittently with no consistent trigger
The code appears sporadically — on some uses but not others, with no obvious relationship to load type, program selection, or duration.
Possible Causes
Internal electronics fault on the control board
An unspecified component on the control board has failed or is operating outside tolerance, triggering the Er18 catch-all fault flag.
Requires ProfessionalIntermittent power supply instability
Voltage fluctuations in the home electrical supply are causing the control board to detect out-of-spec conditions during operation, triggering Er18.
Requires ProfessionalFan or ventilation system obstruction
The internal cooling fan for the magnetron and electronics has become obstructed, causing thermal stress on the control electronics that manifests as Er18.
Requires ProfessionalSafe Checks You Can Do
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1
Perform a full power reset
Switch the circuit breaker off for five minutes and restore power. On Thermador BSH-platform microwaves, a cold restart clears all latched fault flags. Monitor the unit over several subsequent uses to see whether Er18 returns.
If Er18 disappears after a reset and does not return for days or weeks, the fault was caused by a transient event — likely a voltage spike or brief power anomaly. Consider adding a whole-home surge protector.
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2
Ensure the microwave vents are not blocked
Check that the ventilation grilles on your Thermador built-in microwave are not covered by objects placed above or beside the unit. Verify that the installation clearances specified in the use-and-care guide are maintained.
Thermador Professional and Masterpiece built-in microwaves require specific clearances above and on the sides for proper internal airflow. A blocked vent can cause the magnetron cooling fan to work harder, eventually triggering Er18 as a thermal protection response.
When to Call a Professional
Contact a qualified technician if:
- Er18 reappears within a few uses after reset
- Internal fan is audibly louder or slower than normal during operation
- Control board shows signs of heat stress or capacitor bulging on visual inspection
Need Professional Help?
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