Nardi FE0614 Overheating

Hi ive got a Nardi FE0614 Oven that appears to be overheating. The temp dial on the right of the oven does very little. We have to cook everything on 50 otherwise things burn (the misses assures me its not her cooking! ! !) also if doing a roast it tends to cut out after about an hour an half . Im assuming its the thermostat but not too hot on ovens (excuse the pun). Any help would be gratefully appreciated- if it is the thermostat where do i get one and how do i change it also the timer has broke same questions as before please