The toilet will flush but the tank does not fill with water afterwards.

The toilet will flush but the tank does not fill with water afterwards.

Which one of these is your ballcock? Regards, Tom

Thanks for getting back to me. It is the first one (image 400a)

Thanks for getting back to me. It is the first one (image 400a)

OK! You have a FluidMaster Ballcock with a bad seal. Purchase a FluidMaster Seal# 242 ,(see image) Sometimes the orifice in the seal will swell shut and slow the volume of water entering your tank. 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.
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 in above post, ) and pull up. Pry out the seal and replace it. Reassemble, turn the water back on and give it a flush. Better now? Regards and thanks for rating my answer, Tom