Isolating water before plumbing work

Learn to shut off your home's water supply safely and confirm it has actually worked before starting plumbing work.

IW-01Find your stopcockThe stopcock (sometimes called the stop tap) is the main valve that controls all the water coming into your home. Look under the kitchen sink first, then check a utility room, airing cupboard, or an external meter box set into the ground near your boundary or pavement. It's usually a small tap with a round wheel handle or a lever, sitting on a pipe about the width of a broom handle.

IW-02Test it before you need itDon't wait for an emergency to find out your stopcock is seized. Turn it a quarter turn and back again while the water is still on, just to check it moves freely. The beginner mistake is assuming a stopcock works just because it's there - many haven't been touched in years and can be stiff or stuck.

IW-03Turn the stopcock fully offWheel-type stopcocks turn clockwise, the same as tightening - keep turning until it stops moving, using firm but steady pressure, not force. Lever-type valves just need a 90 degree turn so the lever sits across the pipe rather than in line with it. If it feels very stiff, stop and use a bit of penetrating oil rather than forcing it, as a snapped stopcock is a much bigger problem.

IW-04Drain down and release pressureOpen the lowest tap in the house, usually in the kitchen, and let it run into a bucket or the sink. Water flow will slow, then dribble, then splutter as air replaces it in the pipe - that's the sign the pipework has drained. This step matters because pipes stay under pressure even after the stopcock is shut, and skipping it means a surprise soaking when you disconnect something.

IW-05Prove it's actually isolatedOpen the tap or fitting nearest to where you'll be working and check nothing comes out beyond a small dribble. Don't take the stopcock's word for it - some old valves let a steady trickle through even when fully closed. If you still get a real flow after draining down, the stopcock may be worn and unreliable, so stop and get a plumber to fit a new one before you cut into anything.

IW-06Know what the stopcock doesn't coverThe main stopcock only isolates the mains cold water coming into the house. If you have a hot water cylinder fed by a header tank in the loft, that tank can still feed water into pipes even with the mains off, so it needs its own isolation or draining down separately. Never attempt to open up or isolate a gas boiler yourself - by law, any work on gas appliances or gas pipework must be done by a Gas Safe registered engineer.

RULES

KNOW THE RULES

Work on gas boilers or gas pipework must be carried out by a Gas Safe registered engineer, under the Gas Safety (Installation and Use) Regulations.

Save this as a project

Back to all guides