In my airing cupboard is a hot water cylinder.
A 22mm pipe entering close to the bottom of the tank (there's a drain cock on the pipe) has a control tap a bit higher up. If I close this tap off the hot water runs for 30 seconds or so and then stops.
If you have a similar installation you should look for the stop tap you seek on the pipe that enters the bottom of the storage tank.
Good luck...
Peccavi
April 2009