It's an integrated dishwasher and was able to look underneath but couldn't see any signs of leakage. Do you recommend I remove the unit and check behind?
There appears to be a metal cover with screws either side.
I followed your instructions; there was water which I managed to clear; I then tried the machine; it started on its cycle but then stopped after 15 seconds. On checking the settings the code E4 did not show this time, however, there was water in the base again