How can i fix BaumaticBDW13 that overfills & E4 error 5 mins after starting?

A day ago i noticed an inch of water in the bottom of my dishwasher after it had (successfully) finished a program. This has not happened before

I cleared this water out (hard work as water just doesnt seem to be draining fully, unless i used a plunger or similar) but when i tried to restart the machine to check it was working then it just gave an E4 error again and again (even though it seems the drain pump was making plenty of noise and removing any remaining water from the bottom of the machine)

Ive read everyones helpful advice about mopping out the bottom of the machine and resetting the sensor to solve E4 problems. Did this and got it to work again but only until 5 mins into cycle when it was full of water again and E4 error messages (about an inch of water in the main dishwasher and more water down below near the sensors etc)

Can anyone offer any advice as to what the problem/remedy is? I have cleaned the filter and seems fine but cant really get at the pipes that lead to the dishwasher since unit is integrated. Is my only option now to contact Baumatic or a plumber?

Many thanks!