How to Change a Tap Cartridge on a Lever or Mixer Tap

If a lever tap or a quarter-turn tap drips from the spout, the part that has failed is almost always the cartridge, and it is replaced whole rather than repaired. On most taps it is a thirty-minute job with a spanner and a screwdriver. The hard part is not the fitting, it is getting the right cartridge, because they are specific to the tap. Take the old one out first, match it in the shop, then fit it. If your tap has a handle that turns round several times before it shuts, it has a rubber washer instead, and how to change a tap washer is the guide you want.

Which kind of cartridge your tap has

There are two families, and they are not interchangeable.

Tap	Cartridge inside	How it is matched
Two handles, each turning a quarter or half turn and stopping firmly	A ceramic disc cartridge in each side, one for hot and one for cold	Thread size, the number of splines on the spindle, overall length, and which way it closes
Single lever: up and down for flow, side to side for temperature	One mixing cartridge that handles both hot and cold	Diameter, usually 35mm or 40mm, height, the pattern of holes on the base, and the tap's make and model
Thermostatic bath or shower mixer	A thermostatic cartridge	Make and model only. This one is a different job, covered below.

Ceramic disc cartridges come in pairs that close in opposite directions, so the hot and cold handles both turn towards the middle to shut. If you fit a cold-side cartridge on the hot side, the tap works but the handle turns the wrong way. Mark which side each one came from as you take them out.

What you need

• A replacement cartridge, matched to the old one. Do not buy it until the old one is in your hand.
• An adjustable spanner or a deep socket, plus a second spanner or grip wrench to hold the tap body still.
• A flat screwdriver for the isolation valves, and a small crosshead screwdriver or an Allen key for the handle. Lever taps often use a 2.5mm or 3mm Allen key in a grub screw under the lever.
• A cloth to protect chrome from the spanner jaws, and the plug in the basin so nothing small goes down the waste.
• Silicone tap grease approved for drinking water. Ordinary grease is not suitable on a tap you drink from.
• White vinegar or a descaler, if the cartridge seat is crusted with scale.

How to change a tap cartridge, step by step

1. Turn off the water to the tap. Under the basin or sink, look for a small isolation valve on each supply pipe. A quarter turn with a flat screwdriver, so the slot sits across the pipe, closes it. With no isolation valves, turn off the cold at the stopcock, using where is my stopcock if you have not found it before. The hot side is isolated differently on a combi, a cylinder and a tank-fed system, and how to turn off your water supply goes through each.
2. Open the tap fully and let it run dry. That drops the pressure and proves the isolation has worked. Put the plug in.
3. Take off the handle. On two-handle taps, prise off the hot or cold cap on top and undo the screw beneath it. On single-lever taps, the fixing is usually a grub screw at the back or underneath the lever, sometimes hidden under a small plug. Lift the handle straight up off the spindle.
4. Remove any cover. Many taps have a chrome shroud or a threaded collar over the cartridge. Most unscrew by hand. Use a cloth if you need grips.
5. Unscrew the cartridge. It has a hexagon near the top. Hold the tap body firmly with one spanner or grip wrench and turn the cartridge anticlockwise with the other. On a single-lever tap it is usually held down by a large brass nut or a threaded ring rather than being screwed in itself. If the tap body turns on the basin, stop and hold it better, because that twist strains the flexible tails underneath and they are the joint that starts leaking into the cupboard later.
6. Lift it out and look at the seat. Check the rubber seal on the bottom of the old cartridge and the surface it sat on inside the tap. Clean any scale off the seat with a cloth and vinegar. Do not scrape it with anything sharp.
7. Take the old cartridge to the merchant. Count the splines on the spindle, note the hot or cold side, and take a photo of the tap and any maker's name on it. With a single-lever cartridge, the base is the thing to match, as two cartridges with the same diameter can have different hole patterns.
8. Fit the new one. A thin smear of approved silicone grease on the seals, then seat it squarely, with any lugs on the base located in their slots in the tap body. Screw it in by hand, then snug it with the spanner. Firm is enough. Over-tightening a ceramic cartridge can crack it or crush the base seal, and it will then leak or stiffen.
9. Turn the water back on slowly with the tap closed, then open and close it a few times. Refit the cover and the handle, and check the handle stops in the right place. Then check the spout for a drip and the cupboard underneath with dry kitchen paper an hour later.

Why cartridges fail in London

A ceramic cartridge closes by sliding two polished ceramic discs over each other. When the holes line up water flows, and when they do not, it stops. The discs themselves wear very slowly. What usually ends them is scale and grit. London water is hard, as Thames Water explains, and the deposits build up between the discs and on the rubber seals, so the discs no longer meet flat and the tap drips, or the handle goes stiff and gritty. Debris after mains work in the street can do the same thing overnight.

The signs point to the cartridge rather than anything else:

• A steady drip from the spout with the handle fully closed.
• A handle that has gone stiff, crunchy or has started to stop in a different place.
• A single-lever tap that will not hold its temperature, or where the lever creeps down on its own.
• A tap that suddenly will not shut at all, which is usually a cracked disc.

New cartridge, still dripping

If the tap still drips after a new cartridge, one of four things is usually going on.

• The seat in the tap body is scaled or damaged, so the base seal on the new cartridge cannot close onto it. Clean it again and check for a nick in the brass.
• The cartridge is not the right one. A close match that is slightly too short never compresses its base seal. Compare the old and new side by side for height.
• It was not seated square or the lugs were not in their slots. Take it out and refit it.
• The water is not coming from the spout at all. Water around the base of the spout while the tap runs is the body O-rings, not the cartridge, and on a kitchen mixer it runs down inside the unit where you cannot see it. A dripping tap explains how to tell the faults apart and why the base weep is the one to worry about.

If the maker no longer supplies the cartridge, or the tap is old enough that nobody stocks a match, replacing the tap is often cheaper than hunting down a part.

Thermostatic bath and shower cartridges

Thermostatic bar mixers and concealed shower valves also use cartridges, but they do more than open and close. They mix hot and cold to a set temperature, and they carry their own filters and check valves. Changing one is the same in outline, isolate and unscrew, but the temperature stop has to be set again afterwards, and a concealed valve is often only reachable through an access panel. If the problem is a shower that has gone cold rather than one that drips, no hot water in the shower goes through the other causes before you blame the cartridge.

What not to force

• A cartridge that will not move. Scale can bond it into the body. More force usually turns the whole tap on the basin or cracks the body casting, and then the tap has to come out. Stop there.
• A stiff handle. Forcing a stiff ceramic tap cracks the discs, and a slow drip becomes a tap that will not close.
• An isolation valve that will not turn. If it turns but water still comes through, it is passing. Use the stopcock instead.

Is it worth doing now?

A drip into the basin is not an emergency, but on a meter it is water you are paying for, and on the hot side you are paying to heat it too. Reading your water meter shows how to measure what a leak is costing overnight. With the heating season starting, it is also the time to check the outside tap. A drip in October is a split in January, and outside taps before winter covers isolating and draining it.

When to call someone

Hand it over if the cartridge is seized, the tap body turns on the basin when you try, a new cartridge has not stopped the drip, or you find water in the cupboard underneath with the tap off. That last one is the important one. Water under the sink with nothing running is not the cartridge. It is a flexible tail, an isolation valve or the back-nut seal, it is at mains pressure, and it does not stop on its own. A leaking pipe under the sink works through that one.

We repair and replace taps across London, change failed tails and isolation valves while we are there, and put right any damage the water has done to the cabinet or the floor below. We charge £150 per hour, agreed before we attend, with no call-out fee. See water leak repair, or check the pricing page before you call.