How to Find and Test Your Stopcock
There is one job on this website that costs nothing, takes five minutes, and prevents more damage than everything else we do combined. It is finding your stopcock and checking that it turns.
Almost nobody does it. The average household finds out where the stopcock is while standing in an inch of water at eleven at night with a torch, discovering that the valve has not been turned since 2003 and is not going to start now.
Do it on a Sunday afternoon instead.
- Gas Safe registered 981362
- Written from jobs we have actually done
- Milton Keynes and 20 miles around
- 8am – 8pm, Mon to Sat
Last updated
What a stopcock does
It is the valve that isolates the mains water supply to your entire property. Close it and no more water enters the building. That is the difference between a burst pipe that damages a ceiling and a burst pipe that damages a house.
Turn it clockwise to close. The old rule is right: righty tighty.
Where yours probably is
In order of likelihood in Milton Keynes housing:
- Under the kitchen sink, at the back, usually behind the waste trap and whatever has been stored in front of it
- In a downstairs cloakroom or utility room
- Under the stairs, sometimes behind a panel
- In the garage, common on the newer estates
- In a hall cupboard, occasionally alongside the water meter
- Under a floor hatch near the point where the supply enters the building
It will be on the incoming mains, which enters the property at ground level, usually on the wall nearest the road. Follow the pipe from where it comes out of the floor and the stopcock will be on it.
If you genuinely cannot find one, some properties have had them boxed in or covered by later kitchen units, in which case the external stop tap becomes your only isolation and it is worth having an accessible internal one fitted.
How to test it, properly
- 1
Turn a cold tap on, so you can see when the water stops
- 2
Close the stopcock fully, clockwise, without forcing it
- 3
Check the tap. The flow should reduce to a dribble and stop. If it keeps running, the stopcock is not sealing and needs replacing
- 4
Open it fully again, anticlockwise
- 5
Back it off a quarter turn from fully open. This is the bit people do not know: a valve left hard against its stop for years is far more likely to seize there
- 6
Check the tap flow has returned to normal
Do this once a year. Put it in the calendar next to the smoke alarm test.
If it will not turn
The spindle on an old brass stopcock will snap
And then you have a valve that is stuck open and broken, which is worse than one that is stuck open.
Try gentle, steady pressure rather than a sudden effort. Penetrating oil on the spindle and an hour’s patience is worth more than a bigger spanner.
If it still will not move, it needs replacing. This is a small job and it should be done before you need it, not during an emergency.
Your external stop tap
Every property also has an external stop tap, usually at the boundary, under a small metal or plastic cover in the path, pavement or driveway, often marked with a W.
It needs a stop tap key. These cost very little and they are impossible to buy at midnight, so buy one now and keep it somewhere you will find it.
The external tap is your backup when the internal one fails, and it is also what you use if the leak is between the boundary and the house.
While you are there: lift the cover and check it is not full of soil and gravel, because that is how they end up unusable.
Isolating valves: the other five minutes
Beyond the stopcock, individual fittings should have their own small isolating valves, usually with a screwdriver slot, under sinks and behind toilets.
In Milton Keynes these matter more than most places. The water here averages around 300 mg/l of calcium carbonate through Anglian Water, with MK8 at roughly 317 against a UK average of 207, and scale seizes these valves open. When you need one, it will not close, which turns a small repair into a whole-property shutdown.
Test them at the same time as the stopcock. Turn each fully closed and back open. Replace any that will not close.
In an actual emergency
- 1
Close the stopcock, clockwise
- 2
Open the lowest cold tap in the property, usually the kitchen, to drain the pipes down
- 3
If water is near electrics, turn the power off at the consumer unit first
- 4
If the stopcock will not close, go to the external stop tap
- 5
If it is on the heating system rather than the mains, the stopcock will not stop it. Turn the boiler off and close the valves either side of the leak if you can reach them
- 6
Then call. Our emergency page covers the rest
The five minute checklist
- Find the internal stopcock
- Turn it off, confirm the water stops, turn it back on
- Leave it a quarter turn back from fully open
- Find the external stop tap and check the cover lifts
- Buy a stop tap key
- Test every isolating valve under sinks and toilets
- Note where your consumer unit is
- Take a photo of the stopcock location and send it to whoever else lives there
That last one matters. Knowing where the stopcock is does nobody any good if you are the only person in the house who does.
Frequently asked questions
Which way does a stopcock turn off?
Clockwise. Righty tighty.
My stopcock is stiff. Should I force it?
No. The spindle snaps. Try gentle steady pressure and penetrating oil, and if it will not move, have it replaced before you need it.
I turned the stopcock off and water is still coming out. Why?
Either the pipes above the leak are still draining, in which case opening the lowest cold tap will clear them, or the leak is on the heating system, which holds its own water separately from the mains.
Do I need a stop tap key?
Yes, if you ever need the external tap. They cost very little and cannot be bought in an emergency.
Should the stopcock be fully open?
Open it fully, then back it a quarter turn. Fully open for years is how they seize.
My property does not seem to have one.
Some have been boxed in or built over. In that case the external tap is your only isolation, and having an accessible internal stopcock fitted is worth doing.
How often should I test it?
Once a year. Pair it with testing the smoke alarms so you remember.
What to do about it
If yours will not turn
Call 07514 312117. Replacing a seized stopcock is a small job now and an expensive one during a flood. Gas Safe registered 981362, CIPHE member, fully insured, covering Milton Keynes and a 20 mile radius.