there is a motor inside the motorised valves which normally goes, which may need the replacement of the whole 3 port valve, a way of testin it in by turning the stat on the hot water cyclinder down below the temperature of the cyclinder and checkin if the valve closes, or turn the hotwater on and listen for the 3 port valve energizin, if it doesnt id say a new valve, if it energizes then you could be lookin at the room stat
Jazz drummer
January 2009