AEG B4101-4 Electric Oven?

Can anyone give me a clue as to what is causing this problem of the oven cooling fan running permanently? I suspect a cooling fan controller gizmo such as a delay type switch or temperature sensing device which has malfunctioned or gone down. It's a new-ish oven less than four years old and I would greatly appreciate a few pointers on how to identify the faulty part and where to order a new one.
Any honest input will be very welcome!

Cheers.