I have just fitted a new ballcock assembly including flush valve and inlet pipe into my cistern. It fills fine, but when it should stop, it keeps dripping from the outlet into the cistern...I've tried adjusting the ballcock, and changing the height, but no joy. The only way to stop it dripping, shutting the valve completely, is to give the ballcock arm a tap. Then it stops fine.
The valve isn't closing properly. The fact that you can get the valve to stop operating by giving the ballfloat some assistance suggests that it's not the valve itself.
Sometimes you can get this if the ballfloat or the arm is catching on something else in the cistern which prevents it lifting all the way.
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