I have a freestanding Hotpoint Cooker (model HARE60). which has developed a fault on the main oven after around 18 months use. The oven heat up cycles out too quickly so never reaches a temperature which cooks the food. Having assumed that this could only be a fault with the thermostat I have ordered and fitted a genuine Hotpoint part but the problem persists. I assumed this kind of problem could only be the thermostat. Is there some other possible explanation?