Hi guys .Got a heating system with a three port valve controlled by two channel programmer tank stat and room stat.The heating works fine when heating only is selected on the programmer as in the stat will cut it on and off.Hot water works fine when water only is selected it cuts on and off with the tank stat.The problems start when you select heating and hot water at the same time,everything still comes on the water heats up fine and the heating comes on but the stat for the heating will not cut out the result being the rads get to hot