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.
Best Answer
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.