Dishwasher not filling

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 here:
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.
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I suspect the water level switch might be that big white job in the middle of the 2nd pic. You've got a water cavity with what looks like a float that operates it.
I'm guessing you resistance tested the solenoid. Check if its getting voltage when the pwoer is on and wash cycle starting.
NT
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I've had problems with soap and crud getting into the float chamber, so that it thinks it's full when it isnt. The micro switch should be easy enough to test.
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