Why does my bottom oven randomly go off completly. Electrolux EDB710?

The lower oven of my Electrolux EDB710 (w) double Oven is randomly going off. When i use it occassionally (not every time) just the lower oven will go completely off. ie the interior light goes out, the red thermostat light next to to temp control goes off no matter how high a i turn it, and the element begins to cool down. The upper oven works fine and i transfer the cooking into that. But often it will all come back on and appear to work normally.
I don't see that it would be the thermostat as the light also goes out, likewise not the element either. Is there some sort of safety cut out device purely for the lower oven. I've had the back off and can see one but that doesn't appear to relate to just the lower oven. Any ideas please.

Dave
November 2007