how to fix kenwood dishwasher KDW12ST3A?

dishwasher had water in bottom but I tried it and worked but water leaking while it was on then code E4 when i opened it there was a lot of hot water in the bottom and bits of brown debris when I wiped the door seals a lot of dirt came off. I have just moved to this house and inherited the dishwasher. the code means overfilled and cause says too much inlet water could this be because it had not drained properly. Would it help if I used a plunger and then a dishwasher cleaner

Sally Reid
December 2013