My Zanussi ZT 485 built in dishwasher has developed a fault. Whichever cycle you try it, it attempts to pump out water for a couple of minutes and then the "Quick" programme light flashes. i've tried disconnecting the waste pipe from the "drain" end, and it doesn't seem to be blocked but I have yet to try dismantling the machine. The instruction booklet states that the flashing " Quick" light means a problem with the drain, including "There is no vent in the end of the drain hose" . Should I tip the dishwasher over and try to open it up to check the source end of the drain?