Help with water running

Hi,
I'm a total non-plumber, and have a Toto Ultramax toilet. For the past few weeks, we've had to manually stop the water from running by tapping on the blue thing at the top of the tank. Now the problem has gotten worse, and tapping on the blue thing (or putting pressure on it with my hand) no longer works. I've had to turn off the water supply to the toilet.

Can somebody tell me what the problem is and if there's a simple solution? I hate to call the plumber if it's something so simple that I can fix it myself. Thanks for your help.

(Usually) simple solution. Go to Lowes and pick up a cap assembly for around $2 and replace yours. First, though, go to the Korky website and compare their quietfill valve to yours (Toto used that one for many years and only recently switched to a slightly different one). It takes all of about a minute to replace and no tools are required. basically, snap off the top cover, squeeze the tabs on the float and remove, then unscrew a 1/4-turn the cap, then replace everything in reverse. The instructions are on the package.

https://terrylove.com/korky/

Thanks so much, and please bear with me since I don't know the lingo. When you say to replace the cap assembly, are you saying to replace the entire QuietFill valve?

You could do that, but it isn't necessary...http://korky.com/fillvalves.html you can look at the instructions there to. All you probably need is the cap.