Bosch Oven HBN560550B/02 Error Code Er:4

The oven bulb failed and I replaced it with a lower wattage oven bulb I had to hand so we could finish cooking. it was OK for about 10 minutes then with a loud bang the oven died and the MCB tripped. I reset the MCB and the oven display shows Er:4 I looked at the bulb which had exploded/fused internally. On removing the bulb the oven still showed Er4. A quick look on the net indicated that Er 4 is a ” failed temperature sensor” Does anyone have experience with this oven/code? – I find it hard to believe it is a temperature sensor failure!- any help would be greatly appreciated