Hot water spigot

The spigot for the hot water line from above my water heater is leaking. Is there any quick fix for this or is this something that generally warrants the expertise of a plumber? Thanks in advance.

Is the thing labeled a temperature and pressure relief valve? or is it a valve to shut the water off to the heater itself? A clue would be that the pipe coming out of that valve runs to a drain, or sometimes just down to the floor. Once we understand what kind of valve is leaking, we'll be better able to help.