You need to order a new heater element and therostat ( same unit), only about £35, and fitting is very easy- undo the screws to the rear silver cover, this exposes the element which is held in by two screws. The next bit is a bit fiddly but just be slow and patient. Disconect the old unit, then connect the new- just push fit connections. Then screw back on cover and job done.
ian moore
April 2008