How a ceramic disc works
Inside is a pair of very hard, very flat ceramic discs, each with holes. When you turn the handle, one disc slides over the other. Holes lined up = water flows. Holes covered = off. The discs are so flat they seal against each other, and rubber seals at the bottom seal the cartridge to the tap body.
Why they drip
- Grit or limescale scratches the discs.
- The rubber seal at the base of the cartridge wears.
- The cartridge is cracked from over-tightening.
Step by step
- Isolate the water and open the tap to drain.
- Remove the cap and screw (or the hidden grub screw on levers) and pull off the handle.
- Remove any cover shroud.
- Hold the tap and unscrew the cartridge anti-clockwise.
- Match a new one: count the splines, measure the length, note the turn direction.
- Grease the O-rings lightly and fit the new cartridge firmly but not too tight.
- Refit the handle and test.
Pro tip: Sometimes the old cartridge just needs a clean. Rinse grit off the discs and seal and try again before buying.
Single-lever mixer cartridges
Single-lever mixers use one larger cartridge, usually 35mm or 40mm. They are held by a nut or a clamp ring. Match the diameter and the base pattern exactly.
