2 things.... check both wash arms jet holes are clear, remove and wash out under tap...... if residue on plates is still there and appears like a gritty deposit and the water is getting hot then it will be low water level in the machine... usually controlled by a pressure switch with a small air hose on it , trace hose back to a cavity in the sump and it will probably be full of crud. Cheers
Kenjo, March 2014