thermocouple?

I have a baumatic doble oven fan assisted.After 6 months the thermocouple went and replaced by under the warranty.Warranty is now just finished and i get the same symptons as the last time.Oven switches on then upto a certain temperature its cuts off all power to the clock and goes off.After 10 mins everything comes back.Thermocouple requires replacing again same symptons as last time but why does the thermocouple keep going.