neff fan staying on?

My Neff double oven (built-in) normally has a fan that stays on after you switch the heat off to cool it down only now it does not stop at all unless I switch it off at the wall? It is still heating up fine and working but the fan that stays on at the end is still on all the time unless you switch it off at the wall? We did have a fuse go in the house and it has done it since then? What is the fault with this and what part needs to be replaced as it is working just not shutting off when it should? Help