Do you have the model number please.
Also is it onlyt tripping once the door is closed or it is tripping as you are closing the door?
Thanks for that.
Now for a tripping fault it can be a number of things in there thats causing this. But the most common part is either the heater element or the wash motor. These are the most common parts that causes a tripping fault on a dishwasher.
Now cost wise roughly you are looking at about £60 for labour/call out. Then the heater itself is about £80 so thats about £140 all in for a wash heater fault.
Now for the wash motor you are looking at about the £85 mark so again with labour its about £145
Now another option you have is either British Gas or Currys knowhow as they both do a fixed fee repair for about £125. So for that the will call out and replace what ever part it needs and you are looking at the fixed fee price of about £125. You need to contact either of them for there latest prices but they usually are a better option in cases like this as its cheaper through them.
If you need anymore info just get back to me.