I have a large Dimplex XLS Storage Heater which refuses to heat. I have power throughout the appliance - I connected it briefly to the 13 amp ring and placed a tester across all of the switches and elements. It is normally operated via Economy 7 on a 20 amp spur from a consumer unit. Any suggestions please as to what is wrong or which part needs replacing. Its 3 years old in a hallway and may have suffered from having had itemn placed too close to it