Leaking Stopcock or Dripping Stop Tap: Causes and Fixes

Updated July 2026 · Emergency Plumber Chelsea

Start by working out exactly where the water is coming from. Dry the whole valve and the pipe either side with a towel, then wrap a sheet of dry kitchen roll around each part in turn and wait a few minutes. A drip can travel along a pipe before it falls, so the wet spot on the floor is not always under the leak. There are three places a stopcock usually leaks: around the spindle just below the handle, at the compression nuts where the pipes enter each side of the valve, and through the body itself. Each has a different fix.

A leak around the spindle is the most common, especially straight after someone has turned the stopcock for the first time in years. Inside the headgear, the spindle passes through a packing of fibre or rubber held in by a small nut called the gland nut. Turning a stiff old valve disturbs the packing and water starts to weep past it. With a spanner that fits properly, tighten the gland nut, the small nut directly under the handle, by about a quarter turn clockwise. Hold the valve body steady with a second spanner so you do not twist the pipe. Dry it and watch. Often that is all it takes. Do not overtighten; if it takes a lot of force or the handle becomes very stiff to turn, stop.

If tightening the gland does not work, the packing is worn out. On many older brass stopcocks it can be repacked or the headgear replaced, but that needs the water off at a point before the stopcock, which in most homes means the outside stop tap in the pavement or a communal valve in a mansion block. That is usually the point to call a plumber, because if the outside valve does not shut off cleanly you are working on a live mains pipe.

Drips from the compression nuts either side of the valve come from the olives inside the joint. A slight weep can sometimes be cured with a small tightening of the nut, no more than a quarter turn, holding the valve body so it does not rotate. If the joint has been disturbed, the pipe is not sitting straight into the valve, or there is green or white crusting around the nut, the olive probably needs replacing, which again means isolating the supply first. Our guide on how to fix a leaking pipe joint explains how compression joints fail and the stopgap options while you wait.

A leak through the body of the valve, hairline cracks, pinholes or heavy corrosion, cannot be repaired. Neither can a stopcock that no longer shuts off fully, where water keeps trickling from the kitchen tap after you have turned it all the way. The washer inside has perished or the seat has worn, and a stop tap that does not stop the water is not doing its job. Both mean replacement. Old stopcocks in Chelsea's Victorian and Edwardian houses are often decades old, sometimes still on lead or early copper, and they tend to fail the moment they are finally used. If you have lead pipe near the valve, see our lead pipe replacement guide, because it is worth doing both at once.

While you wait for a repair, contain it. Put a bowl or a baking tray under the drip and check it regularly. Wrap a towel round the valve to stop spray. Do not keep opening and closing the stopcock to test it, because each turn disturbs the packing further. If it is dripping from the spindle, leaving it fully open, then turned back a fraction, often reduces the weep, since many old valves seal best at the end of their travel. Do not wrap the spindle in tape or sealant; it will not hold under mains pressure and it makes the proper repair harder.

Some leaks need treating as an emergency. If the drip turns into a steady stream or a spray, if water is running into a floor void, a ceiling below or near electrics, or if the valve body has visibly cracked, you need the water off at the next valve back. For a house, that is usually the outside stop tap under a small metal cover in the pavement, which needs a stop tap key. For a flat, it may be a communal valve controlled by the managing agent or porter. Our guides on turning off your stopcock and shutting off water in a mansion block flat cover where those valves usually are. If you cannot find or turn the outside valve, call a plumber, and if water is leaking from the pavement valve itself, report it to Thames Water, since that side of the supply is theirs.

Replacing a stopcock is a straightforward job for a plumber once the supply can be isolated. On accessible pipework it is often done within the hour, longer if the valve is boxed in, buried in a cellar or on old lead that needs a proper transition fitting. We would normally fit a quarter-turn lever valve or a good quality new stopcock, check the joints under full pressure and show you where it is and how to use it. While we are there, it is worth fitting a second isolation valve if your only shut-off is somewhere awkward, such as under a floor or behind a fitted kitchen. Our guide to stopcock replacement covers what sets the cost, lever valve upgrades and lead pipes in more detail.

A dripping stopcock is also a good prompt to check the rest of your main. If your water bill has crept up, or you can hear water running with everything off, the leak may not stop at the valve. Our guide to reading your water meter shows you how to do a quick overnight leak test, and our water mains repair service covers the supply pipe from the boundary into the house.

If your stopcock is leaking, stiff, or will not shut off the water, call Emergency Plumber Chelsea on 020 3002 6667. We repair and replace stopcocks and stop taps in houses and flats across Chelsea, Knightsbridge, South Kensington, Sloane Square and Fulham, and explain the options before any work starts. There is no call-out fee on jobs over 3 hours. For small drips and other everyday fixes, see our plumbing repairs service.

Quick tips

• Dry the valve and wrap it in kitchen roll to pinpoint where the drip actually starts.
• Spindle leak: tighten the gland nut a quarter turn, holding the valve body steady.
• Joint leak: a small nip on the compression nut may help; crusted joints need new olives.
• Cracked body or a valve that will not shut off fully means replacement, not repair.
• Know where your outside stop tap or communal valve is before you need it.

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