The free diy home improvement guide with answers to your questions on a wide range of do it yourself projects.

Stop Valve – Repair a Leaking Stop Cock

Stop valves or stop cocks as they are commonly called are used for high pressure water supply pipes. A typical example would be the isolation of the incoming mains water in your house. It’s important to know where the stopcock is so that you can turn the water off in an emergency so if you don’t already know where it is, it’s well worthwhile finding out. The most common location is under or near the kitchen sink. Other locations commonly include under stairs cupboards or near the front door.

The stop valve comprises a body and a valve head. When the crutch head is turned, the spindle moves up or down and closes the supply by means of a washer and jumper arrangement over an opening inside the body. As with all valves, it is a good idea to turn them off and on again once a year to make sure they don’t seize up. To reduce the chance of it seizing, after opening it fully, close it again by half a turn and keep it in this position.

Seized Stopcock

If you cannot turn the stop valve off, you can try to free it by using some thin oil – the ones available in a spray can are ideal for this. Lubricate just above the gland nut and allow the oil to penetrate for a while and then try turning the valve head again. If it’s still jammed, slacken the gland nut a little and reapply oil. This should allow the oil to penetrate better. You can apply a moderate amount of force with a wrench but be careful. The head can easily shear off particularly when it’s cold. As a last resort, you can apply a little heat – but only a little. The idea is that metal expands and contracts according to temperature and this can be just enough to free the spindle.

Turning Off the Water

Before carrying out repairs, replacing or moving the mains stop valve in your house you will need to isolate the water supply. This can be done by switching off at the Water Authority’s stop valve out in the street. These can sometimes be difficult to find but are normally in the pavement just outside the boundary of your property. The cover to these is usually marked. If you cannot find it you may need to ask the Water Authority for your area or, have a chat with the neighbours. Note that these valves may also control water to some of your neighbours so you’ll need to let them know before closing it. Depending on the valve, you may need a special key to switch this off

Leaking Valves

If there’s a minor leak from the gland nut (the smaller nut towards the base of the spindle) or one of the compression nuts where it connects to the pipe work, you may be able to stop it without having to turn off the water in the street but make sure you know how to just in case.

Weeping Gland Nut

It water is dribbling very slightly from the gland nut, this can often be stopped by tightening it a little. Make sure you hold the valve body firmly with a wrench while tightening the nut so as not to put any pressure on the compression fittings or pipe work which could make matters a lot worse. If this doesn’t solve the problem, you may need to repack the gland nut.

Leaking Compression Fitting

If there is a minor leak on either of the compression fittings connecting the valve to the pipework, it is sometimes possible to nip this up a little to stop it. Again holding the valve body with a wrench to prevent putting pressure on the pipe work, try gently tightening the compression nut. Don’t over force it though as this could damage the olive on the pipe and create a worse leak.

Replacing the Washer

If the stop valve washer is worn, you may not be able to turn the flow off fully. To replace the washer, you will need to switch off the supply out in the street and drain off the water between the stop valve and the cold water storage cistern, direct taps etc. Check the water is off by opening the kitchen tap. The flow should slow down and stop fairly quickly as the water in the house pipe work drains. Locate the drain valve which should either be an integral part of the stop valve or positioned just above it. Open the drain valve to release the residual water into a suitable container.

Hold the valve body with a wrench and undo the securing nut at the base of the head. Lift out the head and remove the old washer. Fit a replacement washer and reassemble. You can use a little PTFE tape around the thread to ensure a good seal.

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