Dishlex DX302, water solinoid occasionally does not turn off!?

Eco cycle starts with pump out, then water solenoid opens, water flows, then the circulating pump starts and a short period later the solenoid closes. but sometimes it won't and water follows onto the floor. if you watch it you can stop it by turning off the tap under sink for 10seconds and back on, it then finish the cycle fine.
as an electrician I have approached Electrolux and they refuse to supply a wiring diagram.
anyone come across this problem