When something goes wrong with your plumbing — a burst pipe, a leaking tap, or a dodgy appliance — the first thing you often need to do is shut off the water. But here’s where it gets confusing: do you turn the stopcock, or the isolation valve? And what’s the difference anyway?

As engineers working in homes across Exeter and Devon, we’ve found a lot of homeowners aren’t sure which valve is which, or where to find them. So, here’s a clear breakdown of both, when to use them, and what to do if you can’t find either.

The Stopcock (Main Shut-Off Valve)

The stopcock (also called a stop tap) is your main control for water coming into your property. It’s usually located under the kitchen sink, in a downstairs cupboard, or near the front of the house where the mains pipe enters.

What it does:

• Turns off the entire water supply to the house

• Used in emergencies (e.g. burst pipe)

• Important when doing major plumbing work

How to use it:

• Turn clockwise to close, anti-clockwise to open

• If it’s stiff or jammed, don’t force it — that can lead to leaks or damage

Top tip: Test your stopcock once a year. If it’s seized, it’s best to get it replaced before you actually need it.

Isolation Valves (Appliance or Fixture Shut-Offs)

Isolation valves are small inline valves fitted to specific appliances or fixtures — like taps, toilets, washing machines, and boilers.

What they do:

• Control water to just one fitting

• Let you isolate a problem without shutting off the whole house

How to spot them:

• Small silver valve with a slotted screw head

• Usually close to the pipe entering the tap or appliance

How to use it:

• Turn the screw head a quarter turn

• The slot should go across the pipe when off, and along the pipe when on

What If You Can’t Find Either?

If you can’t locate your stopcock or isolation valve in a hurry:

• Check the external stop tap near the pavement — you may need a key or special tool

• Call a local plumber (like EPM) who can locate or replace it

• If there’s a visible leak, shut off electricity in the area as a safety precaution

Final Thoughts

Knowing the difference between your stopcock and isolation valves can save you a huge amount of stress during a plumbing emergency. We’ve seen situations where a quick turn of a valve would have saved thousands in damage.

If you're unsure where yours are, or you'd like them labelled or replaced, EPM can help. We're based in Exeter and cover the surrounding areas — fast, friendly, and clear about what we do.

Want us to check your system? Get in touch — no pressure, no jargon.