Do you have hard water running through the dishwasher? If you are not sure look inside the dishwasher and see if there is mineral or scale buildup. When there is iron in the water the walls will appear light brown or even yellow in color. The best way of knocking the problem out of the inside of the dishwasher is by adding a water softener that is made for the dishwasher. If your dishes still appear dirty after the washing is done, it could be the sprinkler is blocked. The hard water will cause buildup on the sprinkler and clog the holes. The best way of opening the holes back up is by sticking a needle or toothpick in them carefully. This could save you from calling a dishwasher repairs Hampstead