How to isolate a toilet cistern – overflow or maintenance

Need to isolate a toilet cistern? Whether your loo is overflowing and the ball valve won’t shut off, or you turn to isolate the cistern for repair or maintenance, this guide has got you covered.

Turn off the isolation valve near the toilet cistern

This is the fastest way to shut off the water supply, although you will require a slotted/blade-edged screwdriver (the attachment on a pen-knife should be suitable for this).

Simply locate the isolation valve on the supply pipe to the cistern, and turn the screw a quarter turn so that the slot on the screw is no longer in line with the direction of the pipe. This should close the valve.

Tie up the ball valve

If there is no isolation valve, use some string or garden twine to tie the arm of the ball valve to a batten of wood laid across the top of the open cistern. In the event that the cistern is flushed, this will prevent the float from falling and opening the valve.

This method will obviously only work if the ball valve is working, and of course it cannot be used if the purpose of isolating a cistern is to replace the valve inside it.

If there is no isolation valve on the pipework near the cistern and the ball valve is not working or it is impractical to tie it up

Mains-fed toilet cisterns: turn off the mains stopcock, which is typically located under the kitchen sink. This will stop the supply of water to the toilet cistern immediately, notwithstanding any water that remains in the pipework. Note that this will shut off the water supply to every appliance in the household, including the kitchen tap.

Cisterns fed from the cold water storage cistern: close the gate valve on the supply pipe from the cold tank. Note that depending on the configuration of the plumbing system, this may also shut off the supply of cold water to the bathroom.

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