Just moved in to a repossessed house. The whole system had been drained. Switched on the mains so that I could fill header tank . It seems like the water is going straight from header tank in to hot water cylinder then straight out overflow pipe to exterior . I have shut off gate valves at the header tank and filled it up and no water coming through overflow so it's not the ballcock valve. There are 3 gate valves in the airing cupboard and have tried to close them but water seems to be still emptying . Any help greatly appreciated . [/list]