If yours is set up like ours was it has a check valve in the hot water line right at the heater.This valve holds the water from the hot line from going back into the heater when you turn the winterizing valves.I took it out and put a ball valve in its' place to close when winterizing.The spring in it holds it closed when there is very little flowing through the lines so all you get is cold water in the shower hose while it is just dripping.It's a whole lot better to turn an extra valve when winterizing than put up with the cold water surprise.And yes it does work.