Replacing a Tap Washer
You may need to change washers if your taps are dripping or if hardly any water is coming out of the tap once it is open.
1. Turn off the water supply at the stopcock and drain any water from the pipe by opening the tap before removing the top of the tap.
2. Use a flat head screwdriver to lever off the red or blue (hot or cold) indicator cap on the tap. Once the cover has been removed, you will see a screw (image right) that holds the handle of the tap in place around the body. Remove this screw and the handle from the tap.
3. Now use an adjustable spanner to remove the body of the valve by unscrewing anti-clockwise.
4. Remove the screw from the bottom of the valve that holds the washer in place and replace with the new washer. Tighten the screw back into position.
5. Screw the valve back into the tap and use the adjustable spanner to make sure that the valve is tight.
6. Screw the tap handle into position and replace the indicator cap.
7. Refill the system you were working on and check for leaks.
source: mateys plumbing