i appear to have no hot water. I have an indirect water cydlinder. The radiators work fine. Also the header tank appears to have hot water coming into it from the breather. The lower connection of the heating coil in the water cylinder is hot but the one a third of the way up the tank (where it exists) is cold. The only valves are gate valves on the exit and entry of the heating coil. Does anyone have any clues? My only guess is that the gate valve is broken internally or the coil inside the cylinder is blocked. Would this be normal? HELP