Replacing a tap cartridge yourself: step by step

What a cartridge seal actually is

Inside almost every single-lever mixer tap sold in Estonia since the 1990s sits a ceramic disc cartridge. Two discs with slots in them rotate against each other as you move the lever, and the alignment of the slots controls flow and temperature. Older two-handle taps use rubber washers instead, which is a different repair.

When a mixer drips steadily, feels gritty or stiff when turned, or the hot and cold balance has shifted for no reason, the ceramic discs have usually worn, scratched, or picked up limescale grit between them. The fix is not to clean the cartridge but to replace it outright, since the ceramic surfaces do not recover once scored.

What you need before you start

Before buying anything, find the tap's brand and model, usually printed on the underside of the mixer body or on the original box or receipt if you still have it. Cartridges are sold by diameter and by the specific manufacturer's fitting, so a part that looks similar is often not interchangeable.

Shut off the water at the isolation valves under the sink, or at the stopcock if the tap has none, and open the lever fully to release pressure in the pipe before you touch anything.

• Flat-blade screwdriver or hex key, to remove the small set screw under the lever
• Adjustable spanner or a cartridge-specific removal tool, if the mixer needs one
• Replacement cartridge matching the exact brand and diameter (commonly 25, 35 or 40 mm)
• Silicone grease for the new cartridge's O-rings
• A rag and a shallow container, since water trapped in the body will run out
• Descaler or vinegar, useful for cleaning limescale from the seat while it is open

How to remove the lever cap and old cartridge

On most mixers, the lever hides a small screw either underneath it or under a decorative cap on top that pops or unscrews. Once that screw is out, the lever lifts straight off, exposing a metal or plastic collar or dome nut that holds the cartridge in place.

Loosen and remove that collar with an adjustable spanner, taking care not to scratch the chrome finish, then lift the old cartridge straight out. It will usually be seated with two small locating lugs on the underside that fit into slots in the tap body.

Note the exact orientation before lifting it clear, since the new cartridge has to seat the same way for the lever to work through its correct range once reassembled.

Fitting the new cartridge

Rinse the seating inside the tap body with clean water and check for limescale or grit sitting around the two inlet holes, since debris left in place will damage the new cartridge quickly. A soft brush and a little vinegar clears most of it.

Smear a thin layer of silicone grease on the new cartridge's rubber O-rings, then press it into the body with the locating lugs aligned exactly as the old one sat. It should seat with firm hand pressure, not force.

Refit the collar or dome nut and tighten it by hand first, then a quarter-turn more with the spanner, before replacing the lever and its retaining screw.

When to turn the water back on and what to check

Open the isolation valves slowly rather than all at once, and run the tap on cold first, then hot, checking underneath for drips at the collar and at the base of the spout. A cartridge that is not seated squarely will usually leak straight away.

Move the lever through its full range in both directions. If it feels stiff at one end or the hot and cold do not balance the way they used to, the cartridge may be seated a few degrees out and is worth lifting and refitting rather than living with.

When the cartridge does not fit and a new tap is the better buy

Some mixers, particularly older ones or less common brands, use cartridges that are no longer stocked or that need ordering from abroad with a wait of several weeks. If a plumbers' merchant cannot match the diameter and fitting from stock, that is usually the point to stop chasing the part.

At that stage a full replacement mixer, fitted for a fixed quote from 55 € per job, tends to work out cheaper and faster than a special-order cartridge plus the time spent finding one. If you are not confident stripping the tap down in the first place, our plumbing work from 45 € per hour covers this kind of job start to finish, cartridge or full swap.