Where Is My Stopcock And How Do I Use It?

Where is the stopcock in a house?

Look under the kitchen sink first. In a London house the stop tap is usually at the back of that cupboard, behind the bin and the cleaning bottles, on the cold pipe coming up through the floor or the wall from the street. It is a small brass valve with a round crosshead, and the pipe it sits on is cold to the touch even when nothing has been run for hours.

If it is not there, follow the route the mains takes in. The rising main enters at the point nearest the pavement, so a stop tap that is not under the sink is normally near the front of the property. Kitchen refits are the usual reason one goes missing, and a stopcock boxed in behind a new run of units with no access hatch at all is very common.

• Back of the under sink cupboard, on the cold rising pipe
• Downstairs cloakroom, utility room or under stairs cupboard
• Cellar, garage, or under a floorboard just inside the front door
• Boxed in behind kitchen units after a refit, often with no hatch

Where is the stopcock in a flat?

Start at the airing cupboard. If there is a hot water cylinder, the cold feed and the stop tap are very often in the same cupboard, at low level beside or behind the cylinder. After that, check under the bath panel, behind a bathroom or kitchen access panel, and in the hallway cupboard where the meter or the consumer unit lives.

Victorian conversions are the awkward ones. The building was plumbed as a house and then divided, so the original stop tap often still sits where it always did, in the ground floor flat or the basement. Purpose built blocks are more logical: most have a riser cupboard on each landing with a valve per flat, sometimes labelled with the flat number and sometimes only with a faded marker pen. If that cupboard is locked, the key normally sits with the porter or the managing agent.

Blocks with a Pulsacoil or a similar thermal store add one more valve to know about. The unit will have isolating valves on its cold feed and often its outlet, usually in the same cupboard. They are not the stopcock, but they are what you shut if the escape is coming from the store rather than mains pipework.

If the only valve controlling your flat sits in a locked cupboard or in a part of the building you do not control, find out now who holds the key and who to ring out of hours. That number is worth more at two in the morning than any tool you own.

How do I know I have found the stopcock and not another valve?

Close it and run the cold tap at the kitchen sink. That tap is normally the one outlet taken directly off the rising main rather than from storage, so it should run dry within a few seconds if you have the right valve. A traditional stopcock is brass, roughly golf ball sized at the body, with a crosshead and an arrow cast into it showing the direction of flow. Newer installations use a full bore lever instead.

The valves that get mistaken for it are worth knowing, because none of them will isolate the whole property. A quarter turn isolating valve is a small in line fitting with a screwdriver slot serving one tap, toilet or appliance. A gate valve has a small round wheel head and normally sits on low pressure pipework leaving a loft tank. A drain off has a hose spigot and a square nut. A pressure reducing valve has an adjuster and often a gauge.

• Stopcock: brass body, crosshead or lever, on the incoming cold main
• Isolating valve: screwdriver slot, serves one tap or appliance
• Gate valve: round wheel head, usually on pipework from a loft tank

How to turn a stopcock off properly

Turn it clockwise, all the way until it stops, then open the kitchen cold tap to release the pressure in the rising main. A crosshead stopcock takes several full turns to close, not a quarter turn, and partly closing one is the commonest reason people say that turning the water off made no difference to a leak. A lever valve is simpler: a quarter turn from along the pipe to across it closes it completely, and it should never be left halfway, because that wears the seat unevenly.

Turn it by hand with steady pressure rather than sudden force, gripping the handle through a tea towel if it is slippery. With the valve shut and the kitchen tap open, a burst running at full flow should drop to a dribble within a minute as the pipework empties. If the leak is upstairs, open the upstairs taps too, because water sitting above the failure has to go somewhere and you would rather it went down a plughole.

Open it slowly when you turn the water back on. Snapping a full bore valve open sends a pressure surge through the pipework that can knock a marginal joint apart or set off water hammer. Open it most of the way, let the system fill through an open tap, then open it fully.

Do not put a wrench or grips on a stiff stopcock while water is escaping. Old brass valves shear at the spindle, and a snapped stopcock turns a leak you could have contained into one you cannot stop at all. Go to the outside stop tap instead.

Test the stopcock before you need it

Close it fully, check the kitchen cold tap runs dry, then open it fully again. That is the whole test and it takes a minute. Do it once or twice a year and the valve will still work when it matters, because stopcocks seize from sitting still for fifteen years rather than from any fault in the valve.

Hard water is why this matters more in London than in much of the country. Scale builds on the spindle, the gland and the seat of a valve that never moves, and turning it occasionally keeps them clear. Expect a small dribble from the gland nut the first time an old stopcock moves after years of sitting still. That is usually the packing, and a fraction of a turn on the nut normally stops it. If it keeps weeping, the valve is due for replacement, which is better learned on a Sunday afternoon than during a flood.

• Close it fully, confirm the kitchen cold tap runs dry, open it fully again
• Repeat once or twice a year so scale never locks the spindle
• Photograph the location and keep the cupboard in front of it clear
• Show everyone in the household where it is and which way it closes

What to do if the stopcock will not turn

If water is escaping right now, stop trying and go to the outside stop tap instead. Forcing a seized brass valve is how people snap the spindle, and a snapped stopcock during a live leak is genuinely worse than the leak itself. Deal with the emergency at the external valve and come back to the internal one afterwards.

If nothing is leaking and you are simply testing, you have room to be patient. Penetrating oil on the spindle and around the gland nut, left for a few hours, frees a surprising number of them, and small back and forth movements work better than forcing it to travel in one go. What does not work is a long lever. The force available from a pair of water pump pliers is far more than an old casting needs to fail, and it fails without warning.

A stopcock boxed in behind kitchen units or stuck under a sealed bath panel is in the same category as a seized one. If you cannot reach it in ten seconds in the dark, it will not help you, and cutting an access panel into the boxing is worth arranging.

A stopcock that will not close turns a small leak into a burst pipe repair, because the only remaining options are the outside stop tap or waiting for the water company while the water keeps running.

The stopcock turns but the water keeps running

That usually means the valve is no longer sealing internally, and the fix is a new valve rather than an adjustment. Inside a traditional stopcock is a jumper carrying a rubber washer that presses on to a brass seat. The washer hardens with age, the seat pits and scales, and eventually the valve closes without shutting off flow.

Rule out the two simpler explanations first. Make sure it really is fully closed, because stiff old valves feel closed before they are. Then check whether the water still running is coming from storage rather than the main. A cylinder holds a couple of hundred litres and a loft tank a similar order of volume, and the stopcock empties neither, so water on the hot side carries on long after the mains is isolated. That looks exactly like a failed stopcock.

If it is genuinely passing, isolate at the outside stop tap while the internal valve is changed. Most engineers will fit a full bore lever valve in place of the old crosshead, because a lever operates faster under pressure, has no washer to harden, and is far less prone to seizing over the following decade.

Where the supply pipe itself is the problem rather than the valve, the answer sits on the water company side of the boundary or in a no dig pipe repair across the garden, and neither is something a stopcock can help with.

Where is the outside stop tap and how do you use it?

It sits under a small cover in the pavement, path or driveway, normally within a metre or two of the boundary, at the bottom of a narrow chamber. You reach it with a stopcock key, a long T shaped tool with a slot in the end, because the valve is too deep to touch by hand. It also closes clockwise, over several turns.

Lift the cover with a screwdriver, clear the leaves and grit out of the chamber, then lower the key until the slot engages over the crutch on top of the valve. That is slow work in the dark, which argues for lifting the cover once in daylight and checking your key fits. The valve belongs to the water company, and you are entitled to use it in an emergency. In a terrace, one chamber occasionally serves two properties through a shared supply pipe, so closing it can take a neighbour off too.

Buy the key now. They live happily in a kitchen drawer and there is no substitute at the moment you need one. A screwdriver and a broom handle will not engage the crutch, and you will only prove that while standing over an open chamber in the rain.

If the chamber is flooded, silted up, has a broken cover, or the valve will not move, report it to your water supplier rather than digging around in it. That section of supply is theirs to maintain and they will attend to a stop tap that cannot be operated.

What a stopcock does not switch off

The stopcock stops water arriving. It does not empty anything already stored and it has no effect on a supply that is not yours. That distinction explains why a leak sometimes carries on after the valve is shut.

A hot water cylinder holds its full volume regardless of the mains position and keeps feeding a hot side leak until you close the valve on its cold feed, at the bottom of the cylinder on the pipe entering it. A loft tank behaves the same way, and the gate valve on its outlet is what stops that. Heating water is a separate circuit again: rusty brown or metallic smelling water comes from a radiator, a valve or heating pipework, and closing the valves at each end of that radiator stops it.

In a flat, your stopcock controls your flat only. If water is coming through your ceiling and none of your own outlets explain it, the valve that needs closing is upstairs, so knock on the door, then contact the building manager or freeholder who can close a riser valve for the stack. Water travels along joists, so the stain on your ceiling is often several metres from the failure.

Closing the stopcock also proves nothing about where the water has been going, which is why a leak with no visible source ends up as leak detection and repair rather than as a valve you can simply turn.

A hot water cylinder leaking will often keep dripping for a while after the mains are off, because the stored water in the vessel has to find its way out before the flow stops.

• A cylinder keeps feeding a hot side leak until its cold feed is closed
• A loft tank keeps feeding until the gate valve on its outlet is closed
• Brown or metallic smelling water is heating circuit water, not the main
• Your stopcock does nothing about a leak in the flat above you

When a stopcock should be replaced

Replace it when it is stiff, weeping, passing water when closed, or buried somewhere you cannot reach. Any one of those means it will not do its job on the night you need it, and a stop tap that cannot be operated in an emergency is the same as not having one. In London the usual culprit is decades of scale on a valve nobody has moved.

The standard replacement on accessible copper is a full bore lever ball valve, fitted in compression or soldered depending on the pipe run. A drain off immediately downstream is worth fitting where there is space, because it makes every future job on that system faster. The work means isolating outside, draining the section, cutting out the old valve and fitting the new one. Where the stop tap is boxed in, buried in a wall, or the incoming pipe is old lead or steel, it becomes a longer job.

Our engineers are asked to find or replace a stopcock most often on an emergency visit, after somebody has already spent twenty frantic minutes looking for it. It is much better work to do calmly, in daylight, with the cupboard emptied. With 20 engineers covering London it can usually be picked up alongside another job, so it is worth asking while an engineer is already in the property.