If you are talking about relief on top of boiler it is not normal for it to leak. You must never i repeat never seal a safety relief of any kind your boiler could explode. Any time a safety "pops off" there is a problem that needs to be corrected
I'm thinking this is a gag thread... no one could be dumb enough to suggest capping off a pressure/ temp relief valve. We always cut the blowdown pipe at an angle so that joe homeowner cannot cap it off. If the boiler has a domestic coil it could be leaking into the vessel or the pressure reducer could be weak or it could be exceeding temperature. Turn off the water supply to the dom. coil if it has one .. watch the guage and go from there. At the risk of sounding redundant; do not, I repeat, do not cap off a safety valve.. you are putting yourself and your family at great risk..call someone qualified to check this situation out.. dont worry about saving a buck , worry about saving your life! oh and one more comment .. tell the tech who told you to cap it off to think about a career change.
Always tell the truth and you never have to remember what you! said!
not for long with the relief valve plugged ----whats your address i would like to submit a bid--with your "estate" rebuilding your house and replacing the heating system --seriously though -with the relief valve plugged you have a time bomb in your basement --please have it fixed--