The stopcock is the valve you rely on when something else leaks, so it is unsettling when the stopcock itself starts dripping. Most leaks at a stopcock are small and come from a short list of places. Some can be dealt with carefully by a householder. Others need the water shut off further back, at the boundary, before anyone can work on them. And sometimes the water pooling around the stopcock is not coming from the valve at all, but from the supply pipe beneath it.
This guide covers where stopcocks leak, what is safe to try, how to isolate the supply when the stopcock cannot be used, and how to recognise a supply pipe leak.
Where does a stopcock usually leak from?
The traditional brass stopcock found in many London homes has a body with a pipe joint on each side and a spindle coming out of the top, turned by a crutch handle. Each of those parts can leak.
| Where the water appears | Likely cause | Usual next step |
|---|---|---|
| Around the spindle, under the handle | Worn or dried-out packing inside the gland nut | A careful adjustment of the gland nut, or repacking by a plumber |
| At the nut on either side of the body | A weeping compression joint, often after the pipe has been moved | Remaking or replacing the joint, which usually needs the supply off further back |
| From the body itself | A crack, corrosion or frost damage | Replacing the stopcock |
| Water still flowing to taps with the stopcock closed | A worn washer or jumper inside, so the valve does not seal | Rewashering or replacing the valve |
| Below the stopcock, with the valve and joints dry | The supply pipe or a joint under the floor | A meter test and leak investigation |
Before deciding which applies, dry the stopcock and the pipe with a cloth and watch where the first bead of water forms. Water from the spindle runs down the body and can look like a joint leak.
Why does an old stopcock start leaking after it has been turned?
This is the most common stopcock leak of all. A brass stopcock that has sat untouched for years is often sealed around the spindle by packing that has hardened in place. It holds while nobody moves it. The first time someone turns the handle, the packing is disturbed and water starts to weep past the spindle, sometimes only while the valve is part-open.
Two habits reduce the risk. Turn an old stopcock gently rather than forcing it, and once it is fully open, turn it back a small amount so it is not jammed against its stop. If the handle will not move with reasonable hand pressure, do not use a wrench or extra leverage on it. A stopcock forced past its limit can shear the spindle or crack the body, which turns a drip into a flood with no quick way of stopping it.
Can you fix a stopcock leaking from the gland nut?
Often, yes, at least for a while. The gland nut is the small nut on the body just below the handle, through which the spindle passes.
- Identify the right nut. It is the one around the spindle, not the larger nuts on the pipe joints.
- Hold the body still. Support the stopcock with one spanner or grip so the pipe does not twist.
- Tighten a little. Turn the gland nut clockwise a small amount, a quarter turn or less, then check whether the weep has stopped.
- Test the handle. The handle should still turn. If it has become very stiff, the nut is too tight and should be eased back slightly.
- Watch it. Leave kitchen towel under the spindle and check it over the next day.
If tightening does not stop the weep, the packing needs replacing. That is usually done with the supply off, by a plumber, and many plumbers will suggest replacing an old stopcock at the same time with a modern valve that is easier to operate.
How do you turn the water off when the stopcock is the problem?
If the stopcock itself is leaking badly, or the fault is on its body or joints, it cannot be used to isolate itself. The water has to be shut off further back.
- The outside stop tap. Most properties have an external stop tap, usually under a small cover in the pavement or front garden near the boundary, sometimes alongside the water meter. It is normally the water company's fitting and is turned with a long stopcock key.
- A shared supply. In some terraces, conversions and blocks, one external valve serves more than one property. Closing it cuts off your neighbours as well, so speak to them first where you can.
- A valve in a communal area. In flats, your supply may be controlled from a riser cupboard, a basement or a meter cupboard, which the managing agent should be able to identify.
The Water Supply (Water Fittings) Regulations 1999 require a supply to separate premises to have a stopvalve that lets that supply be shut off without shutting off anyone else. Older properties do not always match that, which is why it is worth finding and testing your valves before an emergency. If the outside stop tap is buried, stiff, broken or shared and you cannot operate it safely, contact your water supplier.
If you need water back on before a repair can be done, our guide to temporary fixes for a leaking pipe explains what can and cannot be relied on.
What if the stopcock does not turn the water off completely?
A stopcock that closes but still lets water through to the taps is said to be passing. Inside, a washer on a loose jumper presses down on a seat. When the washer is worn, the seat is scaled or the jumper is stuck, the seal is incomplete.
A passing stopcock is not a leak into the house, but it matters. It makes it impossible to isolate the property in an emergency, it prevents plumbing work being done safely, and it spoils any pressure or meter test that relies on the stopcock being shut. Rewashering or replacement is a plumbing job that needs the supply off at the boundary first.
How can you tell whether the supply pipe is leaking instead?
Water on the floor around a stopcock is not always from the stopcock. The supply pipe usually rises through the floor right next to it, and a leak on that pipe, or on a joint just under the floorboards, can seep up and pool in the same place.
Signs that point to the supply pipe rather than the valve:
- the stopcock body, spindle and joints stay dry after being wiped, but the floor keeps getting wet;
- the floor or wall is damp around the point where the pipe comes up, or along its route;
- the water meter keeps moving with the internal stopcock closed and nothing else running;
- water pressure has dropped with no change inside the house;
- a damp patch or unusually green area has appeared outside, between the boundary and the house.
The meter test is the key check. If your meter is outside and the dial or display moves while your internal stopcock is fully closed and holding, water is escaping between the meter and the stopcock. Our guide to unexplained high water usage explains how to read the meter properly, and our article on finding a leak on the underground supply pipe covers what happens next. A passing stopcock can confuse this test, so the valve needs to be confirmed as holding first.
Should a leaking stopcock be replaced?
Not always. A gland leak that stops with a small adjustment may not need anything more. Replacement is usually the better option when:
- the body is cracked, corroded or has been frozen;
- it passes water when closed and rewashering is not practical;
- it is seized, or so stiff that it could not be used in an emergency;
- it keeps leaking at the gland after adjustment.
When a stopcock is replaced, it is worth asking for the valve to be positioned where you can actually reach it, not behind a fixed kitchen plinth, and for a drain-off point nearby so the system can be emptied in future.
When should you call a leak detection specialist?
A leaking stopcock you can see is a plumbing job. A specialist is useful when:
- the stopcock is dry but water keeps appearing around it or under the floor nearby;
- the meter moves with the stopcock closed and you cannot see a leak;
- the supply pipe runs under a solid floor, a garden or a driveway;
- you need the leak position documented for an insurer or landlord.
Our water mains leak detection for underground and supply pipe leaks is £300 to £500. Call 020 3912 0200 to talk it through.
Frequently asked questions
Why is my stopcock leaking from the top?
Water from the top of the valve, around the spindle, usually means the packing in the gland nut has worn or been disturbed, often after the stopcock has been turned for the first time in years. A small tightening of the gland nut often stops it.
Is a dripping stopcock an emergency?
A slow drip from the spindle is not usually urgent, but it should be contained and dealt with. A steady flow from the body or a joint, or water reaching electrics, needs the supply shut off at the outside stop tap and a plumber.
Can I turn off the outside stop tap myself?
Many householders use a stopcock key to do this. It is usually the water company's fitting, and if it serves other properties or will not turn, contact your water supplier rather than forcing it.
Why does water still come out of the taps with the stopcock off?
Either the stopcock is passing because its washer or seat is worn, or some taps are fed from a storage tank, which keeps supplying water until it empties. Running the taps shows which ones slow and stop.
How do I know if the leak is from the supply pipe?
If the stopcock and its joints stay dry but water keeps appearing nearby, or the meter moves with the stopcock closed and holding, the supply pipe is the more likely source.
