elba px906 cooker?

I'v had 3 thermostats in the last 6 weeks !!!!!!! My oven used to cut out but always come back on after a few minutes. My fan broke so the repair man came out and put a new one in, while he was there he put a new top and bottom element, and ever since then iv had this problem were it cuts out and never comes back on... what the heck needs to be done to fix it ???????????