Tony, Thanks for your response. I've checked the inlet hose and all filters OK..... Came to the conclusion that the problem was related to the vaccuum switch, but not the switch its-self, as switch operates OK with manual pressure applied.
Have removed the IWMS (whatever that stands for - big blue thing on left-hand side with lots of water channels (NB flooded kitchen when removed, so anyone with similar problem _ BEWARE !!!)... The vacuum switch hoses connect into this unit, so suspect that the problem is related to this.
There seems to be a build up of sediment in this, so next step is to clean out (with pressure hose) and re-build dishwasher (if I can remember where all the hoses and screws go !!), and test.
If this fails --- save up for new dishwasher (as it's a pain in the rear end to wash-up manually !!!)
Dave, October 2005