Dishwasher, Indesit, Model:DG6100/1?

The heater burnt out, it melted the outer casing of the heater! I have replaced the heater and on testing found that the water fill level is low. My question is: What sort of level control is fitted to this model and where is it located? Also, should there be a T.O.C in the heater cicuit because I can't find one.
I noticed that the colour of connector ends of the heater on the original was blue and on the Meloni replacement they are yellow. Has this any significance?