How to Turn the Mains Water Supply Off


Before you can do any plumbing job, whether it’s changing a tap washer or mending a leak, you need to know where to turn the water off. Here, we cover everything you need to know about turning off the hot and cold supplies — but not central heating.

All household plumbing systems contain stopcocks or gate valves for isolating the water supply. The basic procedure is:

♦ Turn off the heating as a safety precaution.

♦ Find the nearest stopcock to the pipe or outlet you want to isolate (this will vary from job to job).

♦ Turn the stopcock clockwise as far as it will go.

♦ Open the tap at the end of the pipe run to drain any water left in the pipework (this may take a few seconds).

Unfortunately, there are no ‘rules’ about where stopcocks might be placed: some houses have more than others, and only rarely is there one for every section of pipe. So before you try to find out which stopcock controls which pipes, have a look at the diagram below, which shows how water flows around the house.

where to turn your mains water supply off


Cold supply

This enters the house under mains pressure. In many systems the pipe then splits into two, one branch serving the kitchen sink cold tap and the other the cold storage tank in the roof. In some systems, however, there is no storage tank; the pipe simply divides into branches serving the different outlets so all the cold water is at mains pressure. The diagram shows a storage tank system, but all systems work on the same principle.

From the cold storage tank, further pipes serve the remaining cold outlets and the hot water cylinder. The water in these pipes is not under mains pressure: it relies on gravity, which means that the higher the tank, the greater the ‘push’ the water gets.


Hot supply

The pressure of the water in the hot pipes is governed by the pressure of the cold water. This is because as the water gets heated in the cylinder or water heater, it rises above the cold water being fed in below it; the pressure of the cold water then literally forces the hot water out into the pipes. In other words, stop the cold water and the hot water stops too — a useful point to remember when there isn’t a stopcock where you’d expect to find one.


Trade Tip

Now’s the time to try

"We always tell people to find out where their stopcocks are as soon as they move into a house — far better to do it when you’ve got the time, than when there’s an emergency and you’ve got a flood to deal with.

As you find each one, turn it off and test which pipes it serves by opening all the likely taps or checking the ballvalves in the cold storage tank and WC cistern.

Its a good idea to label the stopcocks with their function, ie ‘bathroom cold water, so that anyone else in the house can find them in a hurry if they need to."

24. May 2011 by admin
Categories: Heating, Plumbing | Tags: , | Comments Off on How to Turn the Mains Water Supply Off


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