Tap won't turn off: how to stop it and what is wrong

Stop the water now

Most taps fitted in the last few decades have an isolation valve on each supply pipe underneath, usually a small brass or chrome fitting with a screwdriver slot or a little lever. Slot or lever in line with the pipe means open. Across the pipe means closed. A mixer tap has two, one for hot and one for cold, so work out which side is running before closing both.

If there are no isolation valves, turn off the internal stop tap. In most London homes it is under the kitchen sink, but it can be in a downstairs toilet, a utility room, a cellar or under the stairs. Our plan for finding and labelling water isolation valves shows where else to look, and if the stop tap is seized or does not stop the flow, our guide for when an internal stopcock will not shut off explains what to do next.

If only the hot tap is running and the hot water comes from a cylinder fed by a tank in the loft, the stop tap may not stop it. The cold feed into the cylinder usually has its own valve, often in the airing cupboard. On a combi boiler or an unvented cylinder, the hot water comes from the mains, so the stop tap does stop it.

Take the plug out and keep the waste clear while the tap is running. A tap that cannot be turned off, running into a sink with the plug in or a slow drain, can overflow onto the floor and into the room below in minutes.

Why the tap will not shut

The way the handle feels tells you what has failed. A traditional tap takes several turns to open and shut. A quarter-turn tap goes from off to full in a quarter or half turn and stops firmly at each end. A single-lever mixer has one handle for both flow and temperature.

Traditional taps: washers and seats

Older pillar taps and many bath taps close by pressing a rubber washer down onto a brass seat. As the washer hardens and wears, you have to turn the handle harder to stop the water, until eventually it will not stop at all. Replacing the washer is a small job, and our guide on how to fix a dripping tap goes through it step by step.

If a new washer does not stop the flow, the seat itself is probably pitted or scored. A plumber can re-cut it with a reseating tool or fit a replacement headgear. Turning the handle harder on a worn seat will not help and can snap the spindle.

Quarter-turn and lever taps: cartridges

Quarter-turn taps and most modern mixers use ceramic cartridges: two discs with openings that line up to let water through and turn away from each other to stop it. They are hard-wearing, but a speck of grit or a flake of limescale can chip a disc, and then the tap will not fully close however far you turn it. Ceramic discs cannot be repaired, so the cartridge is replaced.

The replacement has to match the original: the right size, the right number of splines where the handle fits, and on quarter-turn taps the right direction of closing, since hot and cold often turn opposite ways. Taking the old cartridge to the merchant, or knowing the tap's make and model, saves a wasted trip. Our guide to whether to replace the tap cartridge or the whole tap helps you decide when the tap is old or parts are hard to find, and the guide to quarter-turn or traditional taps explains the difference if you are choosing a new one.

Handles that spin and taps that are stiff

If the handle turns round and round without stopping, the splines have stripped. First check the small screw under the cap or indicator disc on top of the handle. If it has worked loose, tightening it may be all that is needed. If the splines inside the handle are worn, a new handle fixes it. If the splines on the spindle itself are worn, the cartridge or headgear has to be replaced.

London's hard water makes stiff taps common. Scale builds up on the spindle and the rubber seals dry out, so the tap gets harder to turn until one day it will not close properly. A plumber can strip the headgear, clean off the scale and re-grease it with silicone grease made for drinking water installations, or replace it if it has seized. Forcing a stiff tap with pliers tends to crack the body or snap the spindle.

Sensor taps, outside taps and older fittings

A sensor tap that keeps running is usually a solenoid valve or sensor fault rather than a worn washer. Our guide to a sensor tap not working lists what to report before a repair.

An outside tap that will not turn off can often be isolated at a separate valve on the pipe inside the house, usually where it goes through the wall. Antique, designer and imported taps can be harder to get parts for, so it is worth checking what is available before anything is taken apart.

When to call a plumber

Replacing a washer or a matching cartridge is within reach of a confident DIYer once the water is off. Call a plumber if any of these apply:

• There are no isolation valves and the stop tap will not turn or does not stop the flow
• Your stop tap also turns off neighbours' water, so shutting it affects another household
• Water is running into a cupboard, through the floor or into a ceiling below
• The tap body is cracked, or the spindle has snapped
• You cannot identify the cartridge, or the tap is fitted to a stone or composite worktop that makes removal difficult
• Only the hot tap is running and you cannot find a valve to stop it

What a plumber will do

A plumber will isolate the tap properly, strip it down to find which part has failed, and replace the washer, seat, cartridge or headgear. If the tap is old, badly scaled or parts are no longer made, they will talk you through a replacement tap instead. If there were no isolation valves, it is worth having them fitted while the plumber is there, so next time you can stop one tap without turning off the whole house.

Get a running tap stopped today

Loyal Plumbers covers London and everywhere inside the M25, 24 hours a day, with 10 vans on the road. We repair and replace kitchen, basin, bath and outside taps, fit isolation valves and deal with seized stop taps. Call 020 4652 8585 and tell us which tap it is, what the handle does, and whether you have been able to stop the water.

Our call-out charge is £60, and the engineer explains what they have found and what the repair involves before starting. You can read more about our general plumbing and kitchen plumbing work, or about our emergency plumbing service if water is getting where it should not.