First thing is to make sure the shutoff is fully open. You might take the hose off the filler, (shut the supply off first!), then try directing it into the toilet or a bucket to see if the shutoff and line has some crud in it. If that works, then pop the cover off of the filler, take the float out, take off the cap and lift out the strainer. If you go to the www.korky.com website, they have a picture and instructions...you might have some crud in the valve. Once you flush it out, it should work fine.