Thanks for your reply, but the wiring seems fine as the two connectors are unidirectional! I did not make it clear that this is a condensing dryer, and so the heater element is cooled by passage of air.
I suspect the controller is at fault and is applying current to the heater before the dryer is switched on. Presumably, this is why the original heater unit failed - showed signs of overheating - was burnt out!
Ray
January 2015