Diplomat dishwasher ADP 8322 not draining! ?

Hi, I have a diplomat dishwasher Model number ADP8322 which is around 5 years old and has just come out of warranty.

Basically I have noticed recently that when I open the door there is a pool of water sitting at the bottom. When I go to turn it on again it drains and is fine but then a few days later there will be water there again. After some investigation I realised that when the sink tap is on, it starts filling the dishwasher up at the bottom. I have also noticed that when the dishwasher finishes a load it beeps continuiously instead of just 3 times which it has always done in the past.

There are no digital displays so it doesn't tell me an error code or anything.

Any ideas of what might be wrong?

Many thanks,

Mark