My toilet has started running on after flushing - water continues to enter the cistern from the top of the fill tower, and flow out through the overflow. It's not a "perfect" failure; if I depress the ball-float and let it bounce back up, sometimes that shuts off the valve and the water stops - but it doesn't shut off every time. I don't seem to be able to stop the water by manually lifting the float (to exert more pressure on the valve).

I'm guessing I need to replace the valve that the float controls, but I can't find a definitive answer or instructions - largely because I'm not 100% clear what that specific valve is called (so this might be a duplicate for the same reason - sorry!)

I've attached a picture of the cistern, with the valve I think is faulty marked, in case this helps diagnosis.Toilet cistern

  • 1
    Does lifting the float arm stop the water? It may just be that the float needs to be adjusted because of some flex in the plastic pieces.
    – JPhi1618
    Sep 22, 2017 at 13:43
  • @JPhi1618 It doesn't, no. One of the first things I tried.
    – Chowlett
    Sep 22, 2017 at 14:08
  • 1
    Likely needs replacing then. Luckily, fill valves are cheap and very easy to swap out. You don't even need any tools, just a sponge or towel.
    – CactusCake
    Sep 22, 2017 at 14:15
  • Excellent, thanks. So, I think I need to do the process in this video; and it looks like I want a rubber fill-valve diaphragm probably like this? (I'm not very experienced at this sort of thing...)
    – Chowlett
    Sep 22, 2017 at 20:25

1 Answer 1


It's difficult to tell without a close up photo of the valve however your guess sounds correct. It's possible there's some grit or chalk built up that's preventing the valve from closing fully. Unscrewing the part you've circled may allow you to verify and clean it out. Ensure you turn the water supply to the cistern off before removing the part.

  • considering it is plastic, and these are "cheap" it is certainly worth a shot. This is even more likely in a well based system. Although, since @JPhil1618 asked about the float being adjusted NOT working, tells me its more of a seat issue as you suggest. So why not take a peak and see it is accessible. With the parts off try to flush it (turn water on temporarily (cover as needed) and even try to wrap on it a few times to see if vibration helps. Either way, probably just as quick to replace the assembly.
    – noybman
    Sep 24, 2017 at 0:00
  • Well, I unscrewed it, disassembled it, found it was basically pristine. Realised I'd bought the wrong washer, so reassembled it while I exchanged the washer - and found it miraculously was working flawlessly. So ¯\_(ツ)_/¯.
    – Chowlett
    Sep 25, 2017 at 9:32

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