AEG oven switches itself off after 35 mins

Question

Hi, Since the clocks went back on Sunday and we altered the time on the oven display every time I use the oven it turns off after about 35 mins.  If I leave the oven on it comes back on by itself. The oven light goes out the fan stops and the heat goes.  Is it the timer, the thermostat or what???  Before this it has been working well.  It is about 2 years old and in use every day. It is model no. B41014.
Hope you can help.
Regards Donnava.