Although we have a B1421 the same could apply to your oven.
Yes there is a 'thermal fuse' trip or 'temperature limiter' switch that could be faulty. Search for Bosch part 151326.
This is a safety switch in series with the heating element that breaks the current if the oven gets much too hot. It's located on the rear of the oven compartment so you'll have to remove the oven and back cover to see it, just follow the wire to the element. Ours was just above the fan motor. It has two spade terminals on it and has a screw to hold it in place.
Ours was damaged after the element went pop one day. After replacing the element with a new one it would only reach about 100C before
tripping out, even though the light near the knob thermostat was still on indicating that it was trying to reach the desired temperature.
On dismantling the trip it was fairly blackened inside where it had melted when the element blew, and was only connecting intermittently.
Replacing it cured the problem.
Neil W
February 2011
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