Well, What actually happens is this. The water comes out of the regulator and goes both to the heat exchanger and that valve. When the valve is closed, all the water goes through teh heat exchangers then to the front panel output. When the valve is open, the hot water still goes through the heat exchangers and out through the front. BUT! Cold water also goes to the front panel. So, when the engine is hot and the valve is open, you wont get cold water, you will get warm water. Because the hot and cold are mixing.