The T&P relief valve includes a valve spring which is sealed within a protective chamber configured to contain a first protective fluid. The valve spring is protected, by the protective chamber and first protective fluid, from corrosion, calcification and/or mineral deposits which would affect the valve assembly. A thermal element assembly is carried by an internal tongue of the valve casing. A plunger casing is configured to contain a second protective fluid to protect the upper end and captive plunger from corrosion, calcification and/or mineral deposits which could affect the thermal element. The protective chamber includes a sealing flange at a top thereof. An end cap assembly includes an end cap secured to the flange of the valve casing with the sealing flange of the protective chamber therebetween to define a casing seal for the protective chamber and the open top of the valve casing.