Same problem for months. It doesn't refill as normal unless I turn off the water and turn it back off. If I turn the water back on too fast after turning it off it doesn't work. If I give it at least one breath of time off it will work. Almost as if some kind of pressure needs to be relieved.

Hi mayor619 and Welcome to The Plumbing Page. At AskMeHelpDesk.com. You're responding to a 5 year old dead thread so I gave you one of your own. Look in then upper left hand corner of the first post form the date in the first post before you post, Thanks,
Which ballcock is yours?

I'm not the OP but I do have the same problem.
I have the ballcock shown on the left - with 400A in the upper corner.
I hope you're still monitoring!
Mike

I'm not the OP but I do have the same problem.
I have the ballcock shown on the left - with 400A in the upper corner.
I hope you're still monitoring!
Mike
Gotcha covered Mike, The seal on this ballcock can go bad, So you have a FluidMaster ball cock. This is a common problem with these ballcocks. They have a small washer with a hole,(see image) in the center that swells shut in time preventing water from entering the tank.
Purchase a FluidMaster Seal#242 from your local big box store. To replace it you will have to shut the water off to the tank and take the tank lid off. Twist the top of the ballcock off counterclockwise, (see image) and pull up. Pry out the seal. Now place a pan over the open ballcock and turn the water on fro a few seconds to flush out the supply, Now replace the seal. Reassemble, turn the water back on and give it a flush. Better now? Regards, Tom