Belling Duel Fuel oven prob

Hi,
I have been to a duel fuel (stove type) Belling Platinum db3. ser: 03001164 which has probs with main electric oven, it works o.k untill its been used on a high heat for a while then cuts out. Cust says if left for 20 mins or so after it cuts out you can use it again but same prop occurs. The cust claims the last time it cut out she couldn’t get it to work for a few days. When i got there it worked first time everytime.
I suspected there must be a cut out on involved but scrolling through the parts list i cant see, my only other though is maybe the contacts on the selector switch may go iffy when it heats up other then i’m a bit stuck.
Any ideas would be greatly appreciated.
Thanks in advance guys.
Ollie.