mixer5 taps?

if the leak is on a fancy new tap.monoblock.then turn mains or isolating valve.

unscrew the small screw located behind the hot and cold emblem on tap.[bue/red cap}front of tap.the handle will then lift off.maybe stuck but be gentle.you will find a brass nut .tighten slightly otherwise remove nut then replace inside part.which costs £10.do no over tighten fittings.

diy expert,heating engineer
December 2012