No heat on Creda Easy Load Condenair ? how to fix?

I have replaced the two thermostats - although both the old and new ones have a circuit across them (so not failed) the heater elements look fine and also pass a current when tested with a volt meter (test each one in turn or all four - same result) Wiring in machine all looks clean with no evidence of burning or other problems - could it be the controller or is there any way to test the heater circuit ?
Many thanks for any advice - otherwise it will have to be anew one!!