Sometime recently my toilet reservoir tank would not stop filling. It fill the tank to its normal capacity until the float is raised. Once that is done it continues to fill really slow. You probably wouldn't notice it unless it was really quiet and then you could hear the flow.

If left alone it would eventually reach the overflow. So it is no a case of the float level being above the overflow. If I was to pull the float up as high as it comfortably goes the flow persists.

The toilet is working normally. During this slow flow the water is not filling in the bowl so this issue should be limited to the resevoir. There are no leaks outside of the tank that I can find so I think the issue is with the ballcock?

3 Answers 3


Most modern fill valves you can turn off the water and remove the cap. Twist the upper valve part and it will unlock showing the seal and mechanism. Place cup over valve tub slowly turn water to toilet on and run 3 seconds and turn off. Reassemble valve by aliging tabs and twisting back on its only a 15 or 20 degree twist so be gentle. Turn water on and test. If you live in a hard water or silty area or just have old galvanized pipes flakes get caught in there all the time. I was buying new valves often till I figured this out. Half the time a valve is leaking it's usually this I have found and you can't imagine the clients that are shocked to just get billed a minimum service call that took under 3 minutes and most of the time if they are close or in my current route of the day I usually don't even charge them nothing more than a bottle of water or a cup of coffee ☺


Your fill valve has become worn out or compromised.

When the float turns off the fill valve, it continues to let through a tiny trickle. This can be because the valve is worn down and no longer fits the valve seat, or because mineral deposits have built up enough to prevent the valve from fully closing.

The best solution in almost every case is to replace the fill valve.

You could try to clean or repair the valve. I do this sometimes because I am terminally curious about these things and I don't mind taking the plumbing apart several times. Once the valve fails partially, though, cleaning and adjusting will only buy some little time before it fails completely.

Modern toilet tank fill valves (and ballcocks, too) are considered to be very inexpensive compared to the labor cost to remove and replace them. It would not be economically worthwhile to design them so they could be repaired.

  • Fluidmaster offers a replacement seal/ homedepot.com/p/… Other mfgrs do too. It is easier to replace the seal than to replace the entire valve. Jun 25, 2017 at 23:14
  • @Jim Stewart: You're correct. I should modify my answer to include the fact that some manufacturers think it is economically worthwhile to design them so they can be repaired. Jun 26, 2017 at 6:25

You can remove the top of the valve by twisting it [usally ccw] and there will be small particles that need to be removed that are keeping the water running because its not sealing good.Works for me.

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