Isolation Valves — Individual Control for Every Fitting

Isolation valves are small quarter-turn valves on supply pipes under sinks, toilets, washing machines, and dishwashers. They let you shut off water to one fitting without turning off the whole house.

🔍 What they look like

Isolation valves have a flat slot — you turn them with a flat-head screwdriver. They're usually chrome or brass, about thumb-sized, sitting inline on a pipe. Open: Slot runs in line with the pipe. Closed: Slot runs across the pipe (90°). This is universal — it never changes.

📍 Where to find them

Under the kitchen sink (on hot and cold supply pipes). Under the bathroom sink and basin. On the supply pipe behind or below every toilet cistern. On hot and cold inlets to washing machines and dishwashers. On the cold feed to your hot water cylinder.

🛠 Why they matter for quotes

Being able to tell a plumber "I've already isolated the water under the sink" saves 10–15 minutes of their time — at £60–£100/hour that's real money. If there's no isolation valve, note it — ask a plumber to add one next time they're doing any work (£5–£10 in parts).

Good to know: If you're getting quotes for a tap replacement, tell the plumber whether you have working isolation valves. It genuinely affects the time and price of the job.

Was this helpful?

General guidance only — not a substitute for professional advice. Always consult a qualified engineer if you are unsure. Gas work must only be carried out by a Gas Safe registered engineer. Unvented (pressurised) hot water systems must be worked on by a G3-qualified engineer. We accept no liability for any loss, damage, or injury arising from the use of this information.

Up next in Valves & Stopcocks

Gate Valves — the older type found near tanks

← All Valves & Stopcocks guides