Bosch SGS55C02GB/01

Been at this dishwasher today, customer has moved from the south of England where the water is as hard as nails, to our lovely soft water up here in Fife, it was lying in storage for a year and a half, when it is swithed on the check water light lights up and the machine fills until the overfill float and switch activates and pumps out until it resets sw and fills again keeping repeating, i have checked everything but i cannot locate a level switch or pressure sw, there is a pressure swith or sensor seems to be located in the supply after the fill valve before it enters the metering tank, i was wondering if this may be the fault and that it may be all gunged up with limesacle due to lack of use, can anybody give me any pointers with this one cheers JJ