Candy CS455 – Not filling to heater level

Hello, I am repairing a Candy CS 455M dishwasher. The problem is the the machine fills for just a few seconds before the level switch operates and the inlet valve shuts. The water level is below the heater. It should now heat the water but the heater does not get hot. I have checked the heater OK and replaced the level pressure switch to no avail. Without a circuit diagram I need some suggestions. It would seem that the heater is not getting hot because it is not immersed in water but the level switch has made so the machine should think it is. Has anybody seen this before, Desparate for help