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Isolation valves: turning off the water to one tap, toilet or appliance
How the small quarter-turn service valves on UK supply pipes work, which way is open and closed, what to do if one is seized or painted over, and when to use the stopcock instead.
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An isolation valve (also called an isolating valve or service valve) is a small valve on the pipe just before a tap, toilet or appliance. Closing it shuts off that one fitting while the rest of the house keeps its water. If you have them, they turn most small plumbing jobs from "turn off the house" into "turn off the toilet".
Where to find them
Look on the pipe, a short way before the fitting:
- under the toilet cistern, on the pipe to the fill valve;
- under a basin or kitchen sink, one on the hot pipe and one on the cold;
- behind the washing machine or dishwasher, where it is usually a tap with a lever or a small knob (see washing machine plumbing);
- on the pipe to an outside tap, inside the house;
- on the pipes to a combination boiler, a water softener or an electric shower. On a boiler, leave them to the engineer: this site does not cover boiler work.
They are often chrome or brass, about the length of a thumb, with a screwdriver slot in the middle. Some have a small lever or a coloured handle instead. Newer flexible tap connectors sometimes have one built in.
In England and Wales, the Water Supply (Water Fittings) Regulations 1999 expect a water system to have "an adequate number of servicing valves" so that water is not wasted when fittings are maintained or replaced. See Schedule 2 of the Regulations. The Regulations and the guidance from Water Regs UK cover how and where; older homes may have none at all.
Open or closed?
- Slot or lever in line with the pipe: open.
- Slot or lever across the pipe: closed.
It is a quarter turn either way. You do not need to force it past that. Use a flat screwdriver that fills the slot, so it does not slip and chew up the edges.
After closing one, open the tap or flush the toilet to check the water stops. Some valves let a little water by when old. If it keeps running, use the stopcock.
If the valve is stiff, seized or painted over
Valves that have not been turned for years often stick.
- Clean the slot. Scrape out paint or scale with a small screwdriver so a good one can sit fully in it.
- Use the right screwdriver. A broad flat blade that fills the slot. A stubby one helps under a basin.
- Gentle, steady pressure. Try a little each way. Do not hit it, and do not use grips on the body: you can twist the pipe or crack the joint.
- Know your fallback first. Before you push hard on an old valve, check you know where the stopcock is and that it turns. If the valve body or joint starts to leak, close the stopcock.
If a valve will not move, or leaks round the slot when it does, it needs replacing. That means isolating the supply at the stopcock and draining the pipe. A plumber can do it quickly, and if you are confident with compression or push-fit joints, it is a common DIY job.
One fitting or the whole house?
| Job | What to close |
|---|---|
| Changing a tap washer or cartridge | The isolation valves under that tap |
| Fixing a cistern fill valve | The isolation valve on the toilet supply |
| Replacing a washing machine | The appliance valve behind it |
| Leak from a pipe between the stopcock and a valve | The stopcock |
| Burst pipe, or you do not know where the water is coming from | The stopcock, straight away |
| Anything on the hot side fed from a loft tank | The valve on the cylinder cold feed, or drain down. Ask a plumber if unsure |
Remember that closing a cold isolation valve does nothing to the hot supply, and the other way round. A mixer tap needs both closed.
Fitting a new one
Isolation valves come in two common joint types for 15mm pipe:
- Compression: brass, with a nut and olive at each end, tightened with spanners.
- Push-fit: the pipe pushes in and is held by a grab ring. Plastic pipe needs a pipe insert.
Both are covered in push-fit vs compression vs solder. Fit the valve where you can reach the slot later, and check the flow direction arrow if it has one. If you would rather have it fitted, our guide to hiring a plumber covers quotes and checks.
Isolation valves at Wickes
Check the pipe size, joint type and whether it suits hot, cold or both before you buy.
We haven't tested this. Figures are as the maker states them (checked 13 November 2026).
Primaflow chrome plated isolating valve, 15mm. A 15mm compression valve in chrome-plated brass with a quarter-turn screwdriver slot. Wickes lists it as WRAS approved and for shutting off the water to taps and appliances.
JG Speedfit 15SVP service valve, 15mm. A push-fit service valve with a quarter-turn screwdriver slot. Wickes says it suits copper and Speedfit PEX or polybutylene pipe (inserts required), hot and cold water, but not central heating.
Which way is off on an isolation valve?
Across the pipe is off. In line with the pipe is on. A quarter turn is all it takes.
Why is water still coming out after I closed the valve?
The valve may be worn and letting by, or you closed the hot instead of the cold. Check both. If it still runs, close the stopcock.
Should I leave isolation valves fully open?
Yes, in normal use. A half-closed valve reduces the flow to the fitting and can make a toilet slow to fill or a tap weak.