Abstract: A valve mechanism especially suited for use in the inlet and outlet conduits of a hot water heater system comprises a pair of cup shaped metallic members positioned within the respective conduit in telescopic relationship to each other with a coil spring concentrically disposed between the outer cylindrical surface of the inner cup shaped member and the inner cylindrical surface of the outer cup shaped member. An annular flange formed integrally with the inner cup shaped member is clamped between two casing members forming the valve body at the intersection of the two casing members and a screw bolt extends longitudinally and centrally within the valving cavity with the screw bolt clampingly secured at its upstream end to the end wall of the outer cup shaped member and carrying a washer at its downstream end which coacts with the end wall of the inner cup shaped member to open and close the valve.