Bosch Exxcel SMS65E32GB check water error, tried everything!

Hi all,

Determined to fix this error ourselves but after 4+ hours of work so far we are reaching breaking point!

Model is a Bosch Exxcel Aquastar 6.0l SMS65E32GB.

Got to nearly the end of a wash (dishes were pretty clean), then check water error light came on.
Since then we had a brief E14 error appear (now cleared), and a brief E15 error (now cleared). We are now back to check water error.

Below is a list of everything we have tried so far:
Turned off power and water
Removed and cleaned drain filters and washer arm
Checked the impeller for any debris (a few odd small soft bits but nothing major found)
Put some bicarbonate of soda and vinegar and boiling water in to the impeller cavity try and clear anything else that could be blocking.

Removed top and side panel, detached and reattached a couple of wire connectors that looked like they were connected to pumps or similar

Checked the inlet pipe for any kinks or blockage (none), checked the inlet valve for any limescale buildup or blockage (none)

Removed the side plastic container completely by unconnecting all the pipes and wires, flushed this container out with boiling water, reconnected everything correctly

Pressed buttons to do a Reset

Tried running all programmes including pre-rinse, auto, eco (none work, all show check water error after 3-5 mins)

It feels like a drain issue, as a small amount of water is always left in the bottom of the dishwasher when we try and run a programme. If so, not sure what to try next.
However not sure if could also be a filling issue as the plastic side panel starts to fill up with water, but only gets to a very low level then stops, display goes to 0:00 and shows check water code.

Any suggestions?