Our 15 year old Bosch dishwasher has stopped filling although the
heater still comes on. I've checked the water inlet valve for
blockages and put a meter across it which has given a reading within
expected range.

Haynes Dishwasher manual suggests a pressure system fault is most
likely but it's pretty vague about how to diagnose/solve the problem
--- "The pressure system has no standard design or location" --- so
I'm struggling to know what I should investigate next.

I can't see an obvious, separate pressure switch but there is a large
plastic matrix behind the side panel.

Photos of innards he

http://img836.imageshack.us/img836/6492/dishwasher.jpg
http://img696.imageshack.us/img696/2971/dishwasher2.jpg

Any pointers as to likely problem / location / solution would be much
appreciated.