Problem with Electrolux built-in oven E0B5630 model?

I have an electrolux electric built - in oven ( model as above) which is around 18mths old and at present works for around 30 mins cooking using the assisted fan element, then unexpectedly just turns itself off. We dont use the timer so, this shouldnt happen, if we leave the oven to cool down it can sometimes then work again for another 30 mins.

A similar problem exists with the top heating element, except it will only work for 15 - 20 mins on average, when used a as grill

As both appear to be working fine when first turned on it seems to me as if there is some temperature / thermostat control within the oven that cuts in after a period. Could this be the case.