HOW-TO GUIDES
How to fix a leaking stopcock
Updated 07/26
By: Olivia Scammell
Reviewed: Kim Staples
If you want to learn how to fix a leaking stopcock yourself, you've come to the right place. Our guide will take a deep dive into the potential issues associated with a leaking stopcock and how you can try to resolve them at home.
Where to find your stopcock and confirm it's the actual source
The three most common causes of a stopcock leak
Step-by-step fixes for each one
Why regular maintenance prevents bigger problems
Who's responsible for internal vs external stopcocks
How to find a plumber to fix or replace it
A leaking stopcock might seem minor, but left alone it can lead to flooding, mould, and water damage that costs far more to put right.
The good news is that most stopcock leaks come down to one of three fixable causes.
Here's how to diagnose and fix them.
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Tools you’ll need for the job
Bucket and towels
Spanner
Water pump pliers
PTFE tape
Spare washer/s
Find your stopcock and confirm the leak
Your home has two stopcocks (also called stop taps):
An external one, usually under a cover near the boundary of your property, which is your water company's responsibility to maintain.
An internal one, typically under the kitchen sink, in a utility cupboard, or wherever the mains pipe first enters the house, which is your responsibility as the homeowner.
If you're not sure where yours is, see our guide on finding your stopcock.
Once you've located it, confirm the leak is actually coming from the valve itself rather than a nearby joint or pipe.
A stopcock stays open at all times to let water into your home, but you can close it fully to shut off the supply, for repairs, maintenance, or in an emergency like a burst pipe.
If it is the stopcock leaking, the water will be coming from one of three places: the compression nuts, the gland nut, or the head gear joint.
Turn your stopcock fully off and back on every few months, even when you don't need to. It keeps the mechanism from seizing up over time, which is one of the most common reasons stopcocks fail when you actually need them in an emergency.
Fixing a leak from the compression nuts
These are located on either side of the water pipes, and if they're leaking, it will be obvious.
Grip the stopcock body with water pump pliers to hold it steady.
Turn the compression nut clockwise with a spanner until the leak stops.
If that doesn't resolve it, turn off the external stopcock and run your kitchen taps until the water drains fully.
Loosen the nut anticlockwise to reveal the metal ring underneath (the "olive"), and wrap it with PTFE tape.
Replace the nut, tighten it, then turn the external stopcock back on and check for leaks.
If the leak persists after this, it's a good point to call in a plumber rather than keep working on it.
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Fixing a leak from the gland nut
It should be obvious if the gland nut is the problem. Its purpose is to create a waterproof seal that prevents water from leaking up the spindle.
The gland nut sits just below the tap handle and forms a seal that stops water travelling up the spindle. Often, simply tightening it resolves the leak.
Try tightening the gland nut first. Go carefully, since over-tightening can stop the stopcock opening and closing properly.
If that doesn't work, the packing inside the gland nut likely needs replacing. Keep the head gear steady with one spanner while using a second to turn the gland nut anticlockwise until it slides up the spindle.
Scrape out the old packing material with a screwdriver.
Wrap new PTFE tape, or fresh gland packing, clockwise around the spindle.
Pack this material into the gland and slide the nut back into place.
Tighten fully, then loosen very slightly to avoid the stopcock seizing.
Open the stopcock fully, then turn it back slightly to help prevent it seizing in future.
If the leak is only coming from the gland nut, you don't necessarily need to turn off the water supply to fix it. Just place a tray or bucket underneath to catch the small flow while you work.
Fixing a leak from the head gear washer
If water still seeps through even when the stopcock is fully closed, the head gear washer has likely worn out.
Turn off the external stopcock and run your kitchen taps to drain the system.
Grip the tap with water pump pliers and use a spanner to turn the large central nut anticlockwise.
Unscrew the tap handle and pull out the spindle along with it.
Replace the old washer with a new one that matches, then wrap fresh PTFE tape just above it and around the base of the spindle.
Refit the spindle into the tap body and tighten the large nut.
Turn the mains supply back on and check the leak has stopped.
If it hasn't, this is worth handing to a plumber, since replacing the head gear joint itself is a more involved repair.
When to call a plumber
Most stopcock leaks are fixable with basic tools, but it's worth calling a plumber if:
Tightening and repacking hasn't stopped the leak
The stopcock won't fully open or close
Access is restricted, for example under flooring or behind fixed cabinetry
Your home has older pipework, including lead or mixed materials, which may need extra care
You'd rather not risk flooding a kitchen cupboard while you learn
To get started finding a plumber, just enter your postcode into our search tool to browse plumbers who work in your area.
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FAQs
If it's the gland nut causing the leak, tightening it is usually the first and simplest fix. If tightening alone doesn't work, the gland packing likely needs replacing.
Common causes include general wear and tear, pressure build-up over time, or an older stopcock that was never serviced. Regularly turning the stopcock on and off helps prevent this kind of wear.
The property owner is responsible for the internal stopcock, usually located under the kitchen sink. Your local water company is responsible for the external one, typically found near the property boundary.
If the leak is specifically from the gland nut, yes, you can often work on it with the water still on by placing a tray underneath to catch the flow. Leaks from the compression nuts or head gear washer require the supply to be drained first.
Turning it fully off and back on every few months is good practice. It prevents the mechanism seizing up, which is one of the most common reasons stopcocks fail to work when you actually need them.
Many homeowners are switching to lever (quarter-turn) isolation valves when replacing an old stopcock, since they're easier to operate and less prone to seizing than traditional designs. A plumber can advise whether this is a good option for your setup.
Whether you need a plumber, a leak detection specialist, or an emergency roofer, you can find vetted, reviewed tradespeople near you on Checkatrade.
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