zanussi z818 not stopping on fill, how to fix?

HELP! my zanussi z818 is not stopping filling with water on any of the program selections. It will drain ok if I advance the control knob but I have to stop the running program or it overfills. Could it be a pressure switch or is there a timer/programmer? Is there a way to test for the fault or a maintance manual that could provide a flow chart for trouble shooting? Any help would be welcome, email me direct on george.shaw@ukf.net. I am in the UK.