Replacing a mixer tap cartridge

A dripping or stiff single-lever mixer tap usually needs a new cartridge — the ceramic disc mechanism inside the tap body that controls flow and temperature. Cartridges are inexpensive (£5–£30) and replacing one is a straightforward DIY job.

Turn off the water supply at the isolation valves under the sink (slot-head screws on the valve body — turn 90° to close). Open the tap to release residual pressure and drain any water in the supply pipes.

Remove the tap handle: look for a small decorative cap on top (prise off with a flat screwdriver), which hides a screw. Remove the screw, then lift the handle off. The cartridge is now visible inside the tap body — usually a cylindrical brass or plastic component.

Note the orientation of the cartridge before removing it (photograph it). Unscrew the cartridge retaining nut (usually a large hexagonal brass collar around the top of the cartridge) with a spanner. Pull the cartridge straight up out of the tap body.

Take the old cartridge to a plumbers merchant or search the brand and model number (usually printed on the cartridge body) online. Buying the correct replacement is important — cartridges are not universal. Match the diameter (most common: 35mm or 40mm), the spline pattern on the stem, and the overall length.

Insert the new cartridge in the same orientation as the old one (align the hot/cold markings), tighten the retaining nut, refit the handle, and turn the water back on slowly. Check for leaks at the supply connections and test the tap for smooth operation before replacing the decorative cover.