Which way does an isolating valve turn to close?

Small in-line isolating valves are everywhere in a modern house — under basins, behind toilets, at appliances — and reading one takes two seconds once you know the convention.

What you'll need

• A flat screwdriver for slotted valves

Step by step

1. Find the valve.A small brass or chrome body in the pipe with a screwdriver slot in the side, or a small lever. Under basins, behind toilet cisterns, at washing machine tails and beside taps.
2. Read the slot.Parallel with the pipe means the ball inside is open and water flows. At right angles to the pipe means it is closed.
3. Turn a quarter turn only.That is the full travel from open to closed. There is no useful part-open position — partly closing one is how people accidentally starve a fitting for years.
4. Read a lever the same way.Lever along the pipe, open. Lever across the pipe, closed. Identical convention.
5. Turn it gently.A valve that has not moved for years may be stiff. Steady pressure with a properly fitting screwdriver; do not force it with a small blade that will chew the slot.
6. Always confirm at the outlet.Open the tap or flush the toilet downstream. A valve that has seized internally can turn while the ball stays put, which is exactly the situation you do not want to discover halfway through a job.
7. Expect a small residual flow at first.The pipework beyond the valve still holds water. A short run-off is normal; a continuing steady flow means the valve is passing.
8. Return it fully open afterwards.Leaving it part-open is a very common cause of a slow tap or a slow-filling cistern later on.
9. Exercise them occasionally.Turn each valve fully closed and open again once a year. They seize from never being used, and a seized valve is useless in an emergency.

Tips

• Use a screwdriver that fills the slot. A narrow blade rounds the slot and makes the valve unusable.
• Label the valves under a sink with a marker — hot, cold, and which appliance. It saves a lot of guessing later.
• If a valve is stiff, it is probably the one you will most need in a hurry. Free it now.

Common mistakes

• Leaving a valve partly closed after a job — It throttles the flow to that fitting permanently. A slow-filling cistern or a weak tap months later is very often traced back to this.
• Trusting the slot position without testing — Old valves can turn without the internal ball turning with them. Always prove it by opening the outlet before undoing any fitting.

If it doesn't work

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