Dripping Taps And The Washer Inside

A tap that drips is not worn out. Something inside it has stopped sealing, and in most designs that something is a single cheap part.

How a tap seals

Water arrives at the tap under mains or tank pressure and is held back by a moving part pressed against a fixed seat. Turning the handle lifts that part away.

In traditional taps the moving part carries a rubber washer, and the seat is a machined brass ring. The seal depends on the rubber deforming slightly against the metal.

Rubber hardens with age and heat, and grit scores both surfaces. Once the washer no longer conforms to the seat, water passes continuously and the tap drips.

Ceramic discs behave differently

Modern quarter-turn taps use two ceramic discs with matching openings. Rotating one disc aligns or blocks the openings, and the seal comes from the discs being lapped almost perfectly flat.

Ceramic does not perish, so these cartridges last far longer, but they are vulnerable to grit and to limescale that prevents the faces closing fully.

They are also not repairable in any practical sense. A failing cartridge is replaced as a unit, and it must match the tap because the sizes and splines vary.

Working out which you have

The handle movement gives it away. A tap that needs several full turns from off to fully open is a washer tap, and one that opens in a quarter turn is ceramic.

Mixer taps with a single lever use a third design, a cartridge containing both hot and cold paths, which again is replaced rather than serviced.

Photographing the tap and taking the old part to a merchant is more reliable than measuring, because visually similar cartridges are frequently not interchangeable.

The order of operations

Isolate the supply first, at an isolating valve on the pipe beneath if one exists, otherwise at the stopcock. Then open the tap to drain the pressure still in the pipe.

Plug the basin before disassembly. Small screws and circlips fall out during the job, and a plughole swallows them permanently.

Handles are usually retained by a screw hidden under a cap on top. Forcing a handle that has corroded on tends to break the casting rather than release it.

When replacing the washer does not fix it

If a new washer still drips, the seat itself is scored. A seat cutting tool re-faces the brass, and the alternative is a seating washer that sits over the damage.

Water leaking from around the spindle when the tap is open is a different fault, in the gland packing rather than the washer, and is tightened or repacked separately.

Where the tap body itself is corroded or the threads have seized into the basin, replacement is the sensible route, and a seized old tap is a common reason to call a plumber.