To check water valve, turn machine on fill, turn to cold water fill. Unplug several times. See if water shuts off immediately, or if it keeps running a little. Or a Lot. Do the same with hot. If it keeps running, replace valve like AJ said. Even if it doesn't, I would replace valve, can't be much else. Depending on you water quality, valve could be plugged internally a little and be causing this. I would highly doubt the machine is powering up itself and turning on valve, but hey, with this electronic equipment anything can happen.