Thermador E121 — Thermador Oven E121 — Control Board Communication Error
What This Code Means
The main oven control unit lost communication with a secondary board (e.g. the user interface or the relay board). Multiple cooking functions may become unresponsive.
Common Causes
- Loose ribbon cable between control boards
- Power surge affecting one or both boards
- Failed control board
DIY Steps to Try First
- Turn off the oven at the circuit breaker for 2 minutes, then restore — power cycling clears most transient communication faults.
- If the display shows E121 immediately after power restore, it is a persistent hardware fault.