Isolate the cold water cistern: how-to guide

Need to isolate the cold water cistern? Whether you need to repair or replace the ball valve, or carry out further work on the low pressure side of your plumbing system, this article will explain several different ways to carry out this simple task.

How to isolate the cold water cistern

Isolation valve/service valve

The cold water storage cistern (and the feed and expansion cistern) are fed from the rising main. Water byelaws require that supply pipe to the ball valve is fitted with an isolation valve or service valve.

Before isolating the cistern, take a look at the arrangement of the feed pipe, especially if the feed and expansion cistern is close to the cold water cistern. If the isolation valve is before a branch or a tee, it may actually isolate both cisterns.

Isolation or service valves are simple to operate, and are opened or closed using a flat-headed screwdriver. When the slot on the screw is in line with the pipe, the valve is open. Turning the screw a quarter turn so that the blade is perpendicular to the pipe will close the valve.

Alternatively, you may find the isolation valve in the form of a stopcock. This will have a brass handle; do not confuse it with a gate valve. Gate valves have red, wheel-shaped handles, and are installed on the cistern’s outlet pipes.

If there is no isolation valve on the supply pipe

If there isn’t a service valve on the supply pipe, another way to isolate the cistern is to turn off the mains stopcock. This is typically located under or near the kitchen sink. Bear in mind that turning off the mains stopcock will not only stop the cold water cistern from filling, it will shut off the water supply in the entire household.

Tie up the ball valve

If there is no isolation valve on the supply pipe, and it is impractical to switch off the mains, then another way of isolating the cold water cistern is to tie up the ball valve. This can be achieved by laying a baton across the cistern and tying the arm of the valve to it with string or garden twine. However, this method obviously cannot be used if the purpose of isolating the cistern is to repair or replace the ball valve.