Are you sure its the thermostat? I have the same problem but an engineer asked me to check whether the BASE of the top oven was gettiing hot as there are 2 elements. I found only the top was working which is why the light was not going out.(it was not getting hot enough). Unfortunately I don't know how to replace it so am getting an engineer in. The element is said to be £25 or so
John
John R, November 2006