How to Fix a Leaky Stopcock

First, find exactly where the water is coming from

Water runs downhill along a pipe, so the wet patch on the floor tells you little. Dry the whole valve and the pipe either side with kitchen roll, then hold a dry tissue against each part in turn and watch which one darkens first. There are four places a stopcock leaks from, and each has a different fix.

• The gland: the small nut directly under the handle, where the spindle enters the body. The most common, and often it starts right after the valve has been turned for the first time in years.
• A compression nut: the larger nut on either side where the pipe goes into the valve.
• The headgear: the big hexagon between the gland and the body, which screws the top of the valve into the bottom.
• The body itself: a weep through the brass, often with a white or green crust, pinholes, or a hairline crack.

Put a bowl or towel under the valve while you work. If the drip turns into a spray at any point, turn the water off at the outside stop valve and stop.

Dripping from under the handle: tighten or repack the gland

Inside the gland nut is a small amount of packing, either a rubber O-ring on newer valves or a wrapped fibre or string packing on older ones, squeezed around the spindle to stop water escaping as it turns. When the valve is moved after years at rest, that packing shifts and the spindle weeps.

Hold the body of the stopcock steady with one spanner or grips so it cannot twist on the pipe, then tighten the gland nut clockwise by a quarter turn with a second spanner. Dry it and watch for a few minutes. Most gland leaks stop there. If it still weeps, go another eighth of a turn. Stop as soon as the handle becomes noticeably stiff: overtightening the gland makes the valve hard to turn and can seize it in the very emergency you need it for.

If tightening does not stop it, the packing is worn out and can be renewed. Turn the water off at the outside stop valve first, because the gland is under full mains pressure. Then undo the gland nut and slide it up the spindle, pick out the old packing with a small screwdriver, and wind a few turns of PTFE tape or proper gland packing string around the spindle, clockwise, pressing it down into the recess. Refit the nut, tighten it gently, restore the water and check for weeps.

Weeping from a pipe nut or the headgear

Most stopcocks join the pipe with compression fittings: the nut squeezes a soft brass ring, called an olive, onto the pipe. A slow weep at the nut often means it has eased slightly, commonly after someone has leant on the pipe or forced a stiff handle.

Again, hold the valve body with one spanner and tighten the leaking nut about a quarter turn with another. Never tighten one side without holding the body, because the whole valve twists and you disturb the other joint. If a quarter turn does not cure it, one more small nudge is the limit. Beyond that you crush the olive and make the leak worse.

If the nut is tight and the joint still weeps, the olive is damaged or sitting on scored pipe. The joint needs remaking with a new olive, which means isolating the supply at the outside valve, draining the pipe and cutting the old olive off. Leaking pipework joints explains the technique.

A weep from the headgear hexagon, between the gland and the body, is the washer between the two halves of the valve. Nipping the hexagon up while holding the body sometimes stops it. If not, it is a sign the valve is old enough to replace rather than rebuild.

Leaking from the body: this one needs replacing

If the water is coming through the metal itself, there is no fix to attempt. The usual cause in older stopcocks is dezincification: ordinary brass is an alloy of copper and zinc, and some water leaches the zinc out over the years, leaving a porous, crumbly copper that weeps. A white, powdery or green crust on the outside of the body is the giveaway, and it is one of the signs of a stopcock that needs replacing.

A cracked body, often from frost in an outbuilding or cellar, or from someone overtightening a nut, is the same story. Do not tape or seal over it and leave it: a weakened body can let go completely, and it is on the one pipe you cannot isolate from inside the house.

Replacement valves are cheap. Ask for dezincification-resistant (DZR) brass or a quarter-turn valve suitable for drinking water. Our guide to replacing a stopcock covers the job, the options and what drives the cost.

Not a leak you can see: the stopcock won’t shut off

Sometimes a stopcock "leaks" without any water outside it. You close it fully and the taps keep running at a thin stream. That is the washer on the jumper inside the valve, which has hardened or worn so it no longer seals on its seat. It is common on valves that have been left open for decades.

A passing stopcock can be rewashered by isolating outside, unscrewing the headgear and fitting a new jumper washer, but on an old valve the seat is usually pitted too, and replacement is the more reliable repair. Until it is done, you have no working main shut-off, so do not leave it long. Our page on a stopcock that won’t turn also covers a handle that spins without closing.

When to stop and call someone

DIY stops being sensible at the point where you would need to take the valve apart under pressure, or where the only way to isolate it is a seized or missing outside stop valve. Call a plumber if the leak is from the body, if the outside stop valve will not close, if the drip is running into floorboards, a ceiling below or electrics, or if the stopcock is in a flat where the outside valve also feeds your neighbours.

An engineer will isolate the supply, or use a pipe-freezing kit to hold the water back if the outside valve cannot be used, then repack, remake or replace the stopcock and test it under full pressure in front of you. The £60 call-out applies at any hour, and the repair price is agreed with you on site before any work starts. Stopcock repair and replacement sets out the visit.