Quarter-turn tap won't turn off — ceramic disc cartridge replacement

Quarter-turn taps (lever handle taps) use a ceramic disc cartridge instead of a rubber washer. The cartridge contains two ceramic discs — one fixed, one rotating — that seal against each other. When they wear, chip, or become gritty, the tap drips or becomes stiff.

Turn off the supply at the isolation valve (under the basin or at the main stopcock). Open the tap briefly to depressurise.

Remove the lever handle: usually there is a grub screw on the underside of the lever accessed with a 2.5mm or 3mm Allen key, or a push-fit cap on top concealing a Phillips screw. Remove the screw and pull off the lever.

Below the handle is a hexagonal cartridge retaining nut — unscrew this anti-clockwise with an adjustable spanner. Pull out the ceramic cartridge — note its orientation (hot taps typically have a left-hand thread; mark top/bottom if unsure).

Take the cartridge to a plumbers merchant to match the size exactly — cartridges are 35mm, 40mm, or 1/2" and come in different configurations. Alternatively, note the tap brand and model and order online (£3–£20 depending on brand).

Insert the new cartridge in the correct orientation, tighten the retaining nut firmly, replace the handle, and restore supply. Quarter-turn taps should now feel smooth and close completely with a quarter turn.