Underground stopcock won't turn — what to do
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The external stopcock (sometimes called the Buffalo box or property stopcock) is the valve in a small underground box near your property boundary that controls your entire water supply. Knowing where it is and being able to operate it is essential in a flood or burst pipe emergency.
Find the box — look for a small metal or plastic lid flush with the pavement or drive, often marked "W" or "Water" or with a blue lid. It is usually within 1 metre of your boundary wall. If you cannot find it, contact your water company who should have records.
To open the lid, use a metal bar or flat screwdriver in the slot. Some older boxes need a specialist stopcock key — a long rod with a square or flat socket at the end (hire from a tool hire company, or your water company may lend one).
If the valve is seized (will not turn with moderate force), do not force it — you may snap the valve stem. Apply penetrating oil (WD-40 or Plus Gas) around the stem, leave for 20–30 minutes, and try again. In some cases the valve needs specialist attention from your water company.
Turn clockwise to close (off), anti-clockwise to open (on). Many external stopcocks are not designed for regular operation and will seize if not exercised occasionally. Once freed, slowly turn it open and closed a few times to exercise it.
If the external stopcock is your responsibility (on your property side of the boundary) and it cannot be freed or is leaking, contact a plumber. If it is on the highway side of your boundary, contact your water supplier — Thames Water, Anglian Water, etc. — as it is their asset to repair.
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Frequently asked questions
Who owns the underground stopcock outside my property?
If the stopcock is within your property boundary, it is your responsibility. If it is on the public highway or footpath, it belongs to your water company. Contact your water company to identify ownership if you are unsure — they can also advise on maintenance or replacement if it is theirs.
How do I exercise an underground stopcock to stop it seizing?
Turn it off and on a few times annually to keep the valve moving freely. Use penetrating oil if it feels stiff. Never force a seized stopcock — you risk snapping the valve stem, which makes it much harder to repair. If it is genuinely stuck, contact your water company (if on the highway) or a plumber (if in your boundary).
What tools do I need to operate an underground stopcock?
A stopcock key — a long rod with a square or T-bar socket at the end — is needed to reach the valve at the bottom of the underground box. These can be hired from tool hire shops for around £5–£15 per day, or bought for £10–£30. Some water companies will lend them to customers.