Everybody should know where their internal stopcock is and it should be turned at least twice a year so it does not seize. A stopcock that will not close, weeps, or does not exist is a genuine risk, because it is the only thing standing between a burst pipe and a flooded house.
Two valves, and they are not the same
There are normally two points at which your water can be shut off, and knowing the difference matters when something has burst.
The internal stopcock
Inside the property, on the incoming main. Most commonly under the kitchen sink, but also found in a downstairs cloakroom, a utility room, a garage, an airing cupboard, under floorboards near the front door, or in a cupboard that has since had a washing machine built into it. This is yours, it is your responsibility, and it is the one you need in an emergency.
The external stop tap
Outside the boundary, usually under a small cover in the path or pavement, often needing a long key to reach. This one generally belongs to the water company and is on their side of the meter. It is a backup, not your primary isolation – and it is frequently silted up, buried under a resurfaced drive, or serving two properties at once.
If you cannot say where your internal stopcock is without going to look, that is the single most useful thing you could resolve this week. Water running through a ceiling is not the moment to start opening cupboards. There is a short guide to locating it – find your stopcock.
Why stopcocks seize, and what to do about it
A traditional brass stopcock uses a rubber washer on a threaded spindle, with a gland packing around the spindle to stop it leaking. Left untouched for years in hard water, three things happen: the spindle threads corrode and bind, the washer hardens onto its seat, and the gland packing dries out. The result is a valve that either will not turn at all, or – worse – turns and then weeps continuously from the spindle because the packing has failed.
The prevention is free. Turn it fully off and fully on again twice a year, then back it off a quarter turn from fully open so it cannot bind in the open position. That is the whole maintenance routine and it takes under a minute.
If yours is already seized, do not attack it with a large wrench. A stopcock forced past its limit can snap at the body or shear the spindle, which turns a minor job into an emergency with the water still running. It is a straightforward replacement, done under a controlled shutdown at the external stop tap.
Replacing a stopcock
A replacement is a short job that needs the supply isolated externally first, which is why it is worth doing as planned work rather than in a crisis. While the main is open, there are a few things worth considering at the same time:
- Fit a lever ball valve rather than a screw-down stopcock. Quarter-turn, far less prone to seizing, and unambiguous – you can see at a glance whether it is open or shut.
- Add a drain point downstream, so the system can be emptied without dismantling something.
- Check what the incoming main is made of. Lead, old galvanised steel and early blue MDPE all have implications, and a stopcock replacement is when you find out.
- Consider a pressure-reducing valve if your incoming pressure is very high. Excessive mains pressure hammers fittings, shortens the life of flexible connectors and makes appliance inlet valves fail early.
- Label it. A tag on the valve is a small kindness to whoever is standing there at three in the morning.
Mains supply work
Beyond the stopcock itself, the incoming supply occasionally needs attention in its own right.
| Situation | What it involves |
|---|---|
| Poor flow throughout the house | Could be a partly closed valve, a scaled-up section, an undersized supply pipe, or a restriction at the meter. Diagnosis first – see low water pressure |
| Old lead supply pipe | Replacement in MDPE. Water companies often contribute to replacing the section on their side, so it is worth asking before you commit |
| Upgrading 15mm to 25mm supply | Frequently needed when moving to an unvented cylinder or a high-demand system. The pipe from the boundary is the limiting factor and no amount of internal work compensates |
| Very high mains pressure | A pressure-reducing valve protects every fitting downstream and quietens the system noticeably |
| Water hammer | Banging when a tap or appliance shuts off. Caused by pressure surge – usually fixed with an arrestor and by securing loose pipework |
If you are planning an unvented cylinder, the incoming main is the first thing to check rather than the last. There is no point specifying a cylinder that can deliver two showers at once if the supply pipe from the street cannot feed it.
Stopcock stiff, weeping, or missing entirely? It is a short planned job and a very bad emergency.
Questions we get asked about this
My stopcock will not turn. Is that urgent?
Not an emergency today, but it means you have no way to isolate the water if something bursts tomorrow. Treat it as something to sort out within weeks rather than months.
Can I turn the water off at the external stop tap instead?
You can, and in an emergency you should if the internal one will not work. It often needs a long key, the chamber is often full of silt, and in some older streets one tap serves two properties – so it is a backup rather than a substitute.
Should the stopcock be fully open?
Fully open then backed off a quarter turn. Left hard against the stop for years it can bind there, and then it will not close when you need it to.
What is a pressure-reducing valve and do I need one?
It limits the pressure entering the house to a set figure. You need one if your incoming pressure is high enough to be stressing fittings – the symptoms are noisy pipework, flexible hoses failing, and appliance inlet valves needing replacing more often than seems reasonable.
Do I need to upgrade my supply pipe for an unvented cylinder?
Sometimes. An unvented system delivers mains pressure to every outlet, but it can only deliver what the incoming main supplies. We measure the actual flow rate at the stopcock before specifying anything, because that figure decides what is achievable.
Who is responsible for the pipe from the street?
Broadly, the water company owns up to the boundary and you own the supply pipe from there to the house, including any part running under a shared drive. It varies, so confirm with your supplier before commissioning work.
What happens when you call
Call and describe it
You speak to an engineer, not a call centre. Most jobs can be narrowed down on the phone.
We look at it properly
A real diagnosis before a price, and a straight answer if it is not worth doing.
A written quote
Itemised, so you can see what you are paying for.
The job, and the paperwork
Certificates where the work needs them, and what will need attention next.
Where we do this work
Across Norwich and the whole of Norfolk. If you are on the edge of the county, call and ask — we will tell you honestly whether we are the right people.
- Norwich
- Wymondham
- Dereham
- Attleborough
- Aylsham
- North Walsham
- Cromer
- Diss
- Loddon
- Long Stratton
- Watton
- King's Lynn
Need this doing?
Call and describe the problem — you will speak to an engineer, not a call centre. Written quotes, no estimates over the phone.