A Thermador steam oven shares the same control board, heating elements, and door-lock system as a standard wall oven, but adds a water reservoir and steam-generating system as an extra set of parts a standard oven simply doesn’t have. When a steam function won’t engage but standard baking still works normally, that points toward the water supply or steam generator rather than the shared electronics.
Before booking a service call for a steam-specific problem, checking that the water reservoir is properly seated and filled is worth doing — it’s a common, non-repair cause of a steam function that won’t start.