do as the above answer says, but also turn off your heating boiler. most common taps have a removable top, unscrew he top with a large suitable spanner taking care not to scratch the chrome off the tap, try wrapping some cloth around the top before putting the spanner on. once you've got the top off you'll see the large nut that holds the tap assembly to the base, unscrew this using a spanner thin enough to get in (you'll see what i mean). Right, so youve got the assembly out of the base, now locate the small screw at the bottom of the assembly, you've got to get that out and change the rubber seal that it holds in, (usually black) make sure you get the correct size.
reassembly of the tap is the reverse of the above.
alan ions, February 2005