Baumatic BDW 10 Error 4?

At the end of a dishwash cycle my Baumatic BDW 10 displays 'Error 4' and beeps continuously. Your answers to Baumatic dishwashers refer to models 13,14,8,4.5,45, but none to model 10. Mine is built-in. I took off the bottom front panel, but there were no black plastic covers. I pulled out the machine and tipped it up, frontwards and backwards but no water ran out. I took off the left hand side panel and found no water in the bottom. I did find the polystyrene float switch which was dry and free when I shook it up and down. I waggled all electrical connectors which seemed OK. I put it back together and the error has gone away (for now?). What do I do next time? In the manual it says that Error 4 is 'Insufficient water pressure or litre counter valve not working'. Mains water pressure here is good and stop tap is fully open. Is there a water filter in machine? What is the grey plastic squarish fitting (no wires) on the water inlet pipe? What is a litre counter valve, what does it look like, where do I find it, and is it easily replaceable, and where do I get a spare?