Mixer basin taps

[ayjay]

I am trying to fit a mixer tap to my basin. it is one of those with the lever which you lift and turn in one direction for hot and the other for cold. the hot side is fine but the cold keeps running even when in the closed position. there is also a loud screeching noise when closed. i was going to take the tap apart to see if thre is some loose fitting inside but i cant see how i can get into it. can anyone help?
thanks

 

[TicklyT]

Just had to dismantle one so I could assemble it (actually I had to take the valve body out to attach the supply hoses)

Depending on the design, the handle may unscrew, revealing a socket head grub screw retaining the top of the valve, or there may be a plastic plug (sometimes the hot / cold indicator) that can be pulled out. There's not a lot in there unless there's something trapped in the valve seat.