How to fix a leaking stopcock

What is a stopcock?

A stopcock, sometimes called a stop tap, controls the entire supply of mains fed water into your home. The tap is always on, allowing water to enter as and when you need it. But the stopcock lets you shut off the supply in an emergency, such as a burst pipe or to carry out plumbing work.

Usually, there are two stopcocks for your home. One is outside your property, probably under a drain cover. It’s the water company’s responsibility to fix it if anything goes wrong.

The second stopcock is inside and can be found at the point where the mains water pipe enters your home. This is often under the kitchen sink but could also be under the stairs or in a downstairs toilet. When this water stopcock leaks, if you own the property, it’s your responsibility to fix it.

Fixing a leaking stopcock

In this guide, we’ll show you how to fix a leaking stopcock tap that’s inside your home.

A stopcock is made up of three main parts:

• Compression nuts: Two compression nuts join the tap to the water pipes on either side.
• Gland nut: This sits directly below the tap.
• Head gear joint: This is the main body of the tap, between the compression nuts.

If you discover a leaking stopcock tap, it’s essential to tackle it immediately, so it doesn’t get worse. First, check the leak is definitely coming from the stopcock and which part it’s coming from. If it’s leaking from one of the nuts, you’ll be able to see the water dripping. If the leak is in the head gear joint, you won’t see the stop tap leaking. What you may notice is that water still comes through your taps when you’ve turned the stopcock off.

If you’re sure it’s the stopcock that’s leaking, follow the steps below to repair it. Though if you’re uncertain, it’s best to call in a professional plumber.

If you think you have a leak somewhere else in your home, use this handy guide to help detect where the water leak is coming from.

Leaking compression nut

There are two compression nuts on a stopcock that join the tap to the water pipes on either side. If one of these nuts is leaking, try tightening it before doing anything else, as this will often stop the leak.

To tighten a compression nut:

• Grip the body of the tap with water pump pliers
• Use a spanner to turn the nut clockwise to tighten it

If this doesn’t stop the leak, the next step is to seal the nut with PTFE tape as follows:

• Turn off the water supply to the stopcock (do this by turning off the stopcock that’s outside your home)
• Drain the pipes by running the kitchen tap
• Grip the body of the tap with water pump pliers
• Use a spanner to turn the nut anti-clockwise to remove it
• Wrap the olive (the metal ring that’s under the nut) with PTFE tape
• Replace the nut and tighten it
• Turn the outside stopcock back on

Leaking gland nut

The gland nut on your stopcock is the nut that sits directly below the top of the tap. It’s packed with a material that forms a waterproof seal to stop water leaking up the spindle.

A leaking gland nut can often be fixed by simply tightening it. But be careful not to tighten it too much as this restricts the stopcock’s ability to open and close. If that doesn’t work, the gland packing inside is probably worn and will need to be replaced.

There’s no need to isolate the water supply when doing this job.

To replace the gland nut packing:

• Use a spanner to hold the large nut on the head gear still. Use another to turn the gland nut anti-clockwise to unscrew it
• Slide the gland nut up the spindle and use a penknife or screwdriver to pick out the old packing
• Replace the gland packing or use PTFE tape. Wrap a few layers of the tape tightly around the spindle in a clockwise direction
• Push the gland packing, or PTFE tape, down inside the gland
• Slide the gland nut over the packing and retighten (but not too tight)
• Open the stopcock fully and then turn it back half a turn. This can prevent it from seizing up
• The stopcock should now operate firmly, not too easily, and be leak-free

Leaking head gear joint

The head gear joint is the main body of the stopcock and is found in between the compression nuts and underneath the gland nut and the tap itself. If you close your stopcock, but water still comes through, then it will be due to the washer inside being worn out. The washer is attached to the end of the spindle of the tap.

To fix a leaking head gear joint, you need to replace the washer inside it.

To replace the washer:

• Turn off the water supply to the stopcock (do this by turning off the stopcock that’s outside your home)
• Drain the pipes by running the kitchen tap
• Grip the body of the tap with water pump pliers
• Use a spanner to turn the large nut in the centre of the stopcock anticlockwise to loosen it
• Unscrew the tap handle and pull the whole handle and spindle out from the body of the tap
• Pull off the old washer from the end of the spindle and replace it with a new one
• Wrap some PTFE tape around the thread at the bottom of the tap spindle, just above the washer
• Push the spindle back into the body of the tap and retighten the large nut

Finding a leaking stopcock can be worrying. But, as you can see, there’s usually an easy and inexpensive fix you can do yourself.

If you’ve tried everything in this guide and you’re still having problems, contact HomeServe for assistance.

Don’t let a burst pipe or blocked drain slow you down. Take out plumbing and drainage cover and get access to a nationwide network of trusted engineers.

Read our disclaimer