How to Fix a Leaking Tap: Washers, Cartridges and O-Rings

A dripping tap is the most fixable leak in the house. It is also the one people live with longest, because the drip is slow, the noise only matters at 3am, and the tap still works. Meanwhile it wastes water, and in a hard-water area it leaves a streak down the basin that gets harder to shift every month.

Most tap repairs take under an hour once the right part is in your hand. Getting the right part is usually the hard bit. So this starts with diagnosis, not spanners.

Where exactly is the water coming from?

Dry the tap with a towel, turn it on and off once, and watch. Leaks come from four places, and each one points at a different part.

• Drips from the spout with the tap off. The seal that shuts the water off is worn or fouled. On older taps that's the rubber washer and the brass seat it presses on. On newer taps it's the ceramic disc cartridge.
• Water seeping round the handle while the tap runs. Water is getting past the spindle seals: gland packing or an O-ring on old taps, the cartridge's outer O-rings on newer ones. It stops when the tap is off.
• A puddle round the base of a swivel spout. Mixer spouts sit on O-rings. Swing the spout enough times and they wear flat, and water creeps out under the collar.
• Water underneath, in the cupboard. Usually not a tap repair at all. It's the connection below: a flexible hose, a tap tail, a fibre washer or a back nut. Those are covered further down.

If you can't tell, put a dry sheet of kitchen roll under each joint for an hour. Paper doesn't lie.

Which tap have you got?

Turn the handle from fully off to fully on and count.

A compression tap that won't shut off unless you lean on it is telling you the washer is finished. A ceramic tap doesn't get stiffer as it wears. It just keeps dripping when it should be off.

Kit

A flat-head screwdriver, two spanners (or a spanner and grips), Allen keys for lever grub screws, a cloth to pad the jaws, silicone grease meant for taps, white vinegar or a citric acid descaler, an old toothbrush, and a small tub for screws in the order they came out. Take a photo at every stage. Don't use petroleum jelly on the seals; it can make some rubbers swell and go soft.

Turn the water off

Look under the basin first. Most modern installations have a small isolation valve on each supply pipe, a little brass or chrome fitting with a slot in the top. Turn the slot a quarter turn with a flat screwdriver. When the slot runs across the pipe, it's off. When it lines up with the pipe, it's on.

No isolation valves? Turn the cold off at the stopcock, usually under the kitchen sink. With a combi boiler, the hot is heated from the mains cold, so the stopcock covers both. With a hot water cylinder, close the valve on the cold pipe feeding the cylinder and run the hot tap until the flow dies away.

Then open the tap you're working on, so what's left in the pipe drains now and not over your wrists.

If the isolation valve hasn't moved in fifteen years, don't force it with pliers. Old ones snap. Use the stopcock instead and replace the valve another day.

Protect the basin

Put the plug in. That one move saves more small screws than anything else here. Then fold a towel into the basin. A dropped spanner will chip ceramic, and a cracked basin turns a cheap job into a dear one.

The repair, step by step

The order is the same for most taps.

1. Take off the cap or indicator. The red or blue disc on top usually prises out with a thin blade. Underneath is a screw or a grub screw.
2. Remove the handle. Undo the screw and lift. If it's stuck on its splines, rock it gently. Brute force snaps plastic handles.
3. Remove the shroud. On older taps a chrome cover hides the headgear. Many unscrew by hand; pad the grips with a cloth if not.
4. Undo the headgear or cartridge nut. Hold the tap body steady with one spanner and turn the nut anticlockwise with the other. Without that second spanner you're twisting the whole tap against the basin, which is how basins crack.
5. Lift out the headgear or cartridge. Note which way round it sat.
6. Replace the worn part. Details for each type are below.
7. Clean inside the tap body. Look in with a torch. Wipe out grit and scale.
8. Reassemble in reverse order. Grease O-rings lightly. Tighten nuts firmly, not savagely. Brass threads strip.

Compression taps: washer and seat

The washer sits on the bottom of the headgear, held by a small nut or pressed onto a button. Prise the old one off and fit the new one. Then look at the brass seat at the bottom of the tap body. It should be a clean, smooth ring. If it's pitted or crusted, a new washer will drip within days, because it's sealing against a rough edge.

If the spindle leaks under the handle, the gland nut (the small nut where the spindle leaves the headgear) can be tightened a quarter turn. If that doesn't stop it, the packing or the O-ring needs replacing.

Quarter-turn ceramic disc taps

The cartridge holds two ceramic discs with holes in them. Turning the handle lines the holes up. The discs don't wear like rubber, but scale and grit get between them and stop them closing fully. Sometimes a soak in vinegar brings a cartridge back. Often it doesn't, and you replace it. Check its outer O-rings while you're there.

Single-lever cartridges

The cartridge is held by a nut or collar, sometimes a pair of small screws. Pull it straight out. Clean the seat it sits in and check the small rubber seals on its base, which sometimes stay stuck in the tap body. Leave an old one in there and the new cartridge won't seal.

Getting the right part

Take the old one to the shop. Not a photo. The part.

Washers come in different sizes for basin taps and the larger bath taps. Ceramic cartridges differ by spline count, length, thread, and which way they turn to open; hot and cold are often opposites. Lever cartridges vary in diameter, height and stem profile. Two that look identical on a shelf can be a few millimetres apart, and a few millimetres is the difference between a tap and a fountain.

No match? Check the tap body for markings and keep the old part to compare.

Limescale on the seat

In hard-water areas the seat and cartridge collect a crust that a new washer can't seal against. Soak removable parts in white vinegar or a citric acid solution for half an hour, scrub with the toothbrush, and rinse well. For the fixed seat inside a compression tap, dab descaler on with a cotton bud, leave it a few minutes, then wipe clean.

A badly worn seat can be ground smooth with a reseating tool, a hand-turned cutter that screws into the tap body, or covered with a plastic seat-and-washer kit. Neither works on a cracked seat. If scale is a constant fight, the guide to hard water and limescale covers the causes and what helps further upstream.

Putting it back and testing

Hand-tighten everything first, then nip up with a spanner. Refit the shroud, handle, screw and cap. Close the tap. Turn the isolation valve back slowly, a little at a time, and watch the new parts as pressure returns.

Then check:

• The spout stays dry five minutes after the tap is off.
• Nothing weeps from the handle while the tap runs full.
• Hot and cold are still on the correct sides and turn the right way.
• Under the basin is dry, especially if you leaned on anything.

Leave a sheet of kitchen roll under the spout overnight. A dry sheet in the morning is your sign-off.

If it still drips, the usual suspects are a damaged seat, a wrong-size washer, or an old seal left behind in the tap body.

Leaks under the basin: flexi hoses and tap tails

Most modern monobloc taps are fed by two flexible braided hoses screwed into the base. They don't last forever. Check yours for:

• Rust spots or broken strands in the braid
• A bulge or kink anywhere along the hose
• Drips at either end, where the hose meets the tap or the isolation valve

A bulging or rusty hose gets replaced, not tightened. The braid is only a cover; the rubber hose inside holds the pressure. Replacing one is quick: isolate, unscrew, fit the new one with its seal, and don't overtighten.

Older pillar taps have rigid tap tails with a fibre or rubber washer and a back nut under the basin. A slow leak there usually means a hardened washer or a loose back nut. Tightening helps for a while. A new washer fixes it.

If the cupboard floor is wet and none of those joints are damp, look higher. The waste trap, the basin overflow and the wall behind can all feed the same puddle.

When it isn't the tap

Sometimes the tap is fine and the water is going somewhere else. The US EPA's WaterSense programme estimates household leaks can waste nearly 10,000 gallons a year, and plenty of that never shows up as a drip. If the bill looks high or you can hear water moving when nothing's on, run a water meter leak test before pulling taps apart. A meter that keeps turning points to a hidden leak, and the leak detection guides explain how to narrow it down.

And know when to stop. A tap body that's cracked, badly corroded, or spins in the basin when you turn the handle needs replacing. So does one that still drips after you've fitted the right part twice. At that point a new tap is the repair, and if the pipework underneath looks tired or non-standard, that's a job for a plumber rather than a Sunday-night experiment.