Temperature and Pressure Relief Valve Leaking?

you need to install the proper expantion tank .... in the proper location..... and you must check the psi. of the new expantion tank to make sure it will work against the existing house pressure... t&p valves come with 3 ratings temp.... press.... and also BTU'S I have seen t&p valves that had the required temp... and press.... blow off because the btu wasnt enough.... sounds crazy but it has happened