Fix a faulty ball valve

A ball valve or float valve controls the flow of water into your toilet system. Old or faulty ball valves that need replacing cause an overflow of water from the cistern pipe causing the cistern to run dry.

Level of difficulty

Level 2: Intermediate

What you need

Ball valve
Lubricant oil

The steps to follow

Note: If your cistern is overflowing, check that the valve is floating. If it is partially submerged, fix the ball valve to the side of the cistern to close the valve with some string or tape.

  1. Unscrew the float and empty the water
  2. To temporarily repair the ball valve, tie a small plastic bag around where the existing ball valve should be. Then, get a new valve to fix the problem permanently, checking which sort you need. The most commonly used valve is the brass Portsmouth with an internal piston. Other types include equilibrium or diaphragm valves
  3. Turn off the water supply to the cistern
  4. If the problem is coming from the toilet cistern, cut off the supply to the cold water storage tank and drain it by turning on the bathroom cold taps
  5. Flush the cistern to drain the supply pipe
  6. If you have a Portsmouth valve, remove the float arm and pull out the securing pin with pliers
  7. With a wrench, unscrew the cap at the end of the valve. If needed, apply lubricating oil to loosen it
  8. Lever out the piston by sliding the blade of the screwdriver in the slot of the valve. With a one-piece piston, simply remove the old washer and replace with a new one. If you have a two-piece piston, rotate the piston and unscrew the cap with a screwdriver to remove the washer. Replace with a new washer
  9. Clean the valve and lubricate the piston with lubricating oil
  10. Reassemble the valve and turn on the water supply
  11. Make sure the cistern fills up just below the warning level
  12. For diaphragm valves, unscrew the retaining nut at the end of the valve body and remove the end cap
  13. Lever out the existing diaphragm with a screwdriver and replace with a new one. Note the way in which the old diaphragm was fitted so that you can insert the new one in the same way
  14. Reassemble the valve and turn on the water supply

Don’t want to DIY? Get recommended plumbers for your home improvement job.

Please note that all our DIY guides and ‘Expert answers’ advice have been written strictly for reference only. Rated People do not accept any liability for any damage caused to an individual, property or anything else as a result of following our DIY guides and using our ‘Expert answers’ advice.

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