Thermador SC301 single electric oven: the oven

Thermador SC301 single electric oven: the oven sounds like it is coming on (e.g., when you hit "bake" and then 350 and "bake"), the fan comes on, the display comes on and says 100 (degrees), but nothing happens. It doesn't heat up. What is bizarre is that this non-performance is erratic. Sometimes you try four times (touching the control panel indicators) and it doesn't work, and then for some unknown reason, on fifth try, the heat does come on.