The simple answer is ( hopefully )... There are two overheat sensors in the back, just above the heater elements. They are about the size of a 10p piece, held in by two screws, two wires going to each. In the middle of each is a little hole. If you push the end of a paper clip into the hole you will hear a click as the one that has tripped resets. They are more likely to trip if you have the drier pushed hard back against a wall with no room behind it for air to circulate... hope this helps !
J.R.Copley, July 2009