Every Thermador Oven Function Worked Except Broil
The broil request produced no ignition activity, and the technician measured no supply at the broil igniter. A recently replaced temperature potentiometer had solved a different error but changed nothing in broil.
Why the mode split mattered
Normal operation in the other modes showed that this was not a completely dead appliance. The fault followed the broil command specifically. That focused the diagnosis on the broil request, its board output, wiring and ignition load rather than on every oven control.
A similar symptom can have a different cause on another oven. A failed igniter, damaged harness, safety device or control input can also prevent broil from starting.
What the unsuccessful replacement ruled out
The temperature potentiometer had been replaced because the oven previously displayed error 21. That error was corrected, but broil remained silent. In the discussion, the potentiometer was identified as serving a different function, so its replacement was not evidence that the broil output had been repaired.
How the technician narrowed the remaining branch
The decisive observation was absence of supply at the broil igniter while broil was requested. With the other modes working, the discussion converged on the broil relay or its board-output path. The board looked normal, but relay failure does not have to leave visible scorching or a shorted area.
The source ended after that diagnosis. It did not document a board repair, relay replacement or successful broil retest.