I have a American Standard Champion 4 toilet I bought & installed 8 months ago. It has been working fine but now it runs intermittently. It flushes and fills fine. It doesn't run constantly. It will run in few second bursts then quit. I wouldn't worry about it but my water bill has jumped up and this is the only thing I have found at this point. What do you think is the problem and how can I fix it?

Hello place a few drops of watering ( food colouring works) in the back of the toilet in the evening and in the morning is the water is coloured in the bowl replace the flabber
Also check the level of the over flow tube once the tank has filled the water level should be below the top by 1/4 of an inch
It could be that the fill valve needs adjustment

What do you think is the problem and how can I fix it?
I think you have a flapper that's leaking and needs to be replaced.
Check the tank water level, it should be at the mark in the tank or 3/8 to 1/2" below the top of the over flow tube. Now look at the flapper, If it has wavy edges on the flat surface, replace it. With the flapper seated the linkage wants to have 1/4" of play. Too much play and the flapper doesn't get pulled back enough giving you a short flush. Too tight and it lets water seep past the flapper. I adjust the chain by the link and if it needs fine tuning, I bend the flush lever rod a bit until I have the desired play in the linkage. One more thing about a flapper. you will see where the old flapper hooks onto the base of the white overflow tube. On a older type with no hooks the flapper has a ring that slips down over the overflow tube to the seat. If your tank has hooks, take a sharp knife or scissors and cut the neoprene ring off on the marks provided and hook the flapper on the hooks. Leaving the ring on will interfere with the flush. The linkage between the flapper and the flush lever should have 1/4" play when the tank is filled. Also, check the small tube coming out of the top of the ballcock and make sure it's connect to and draining into the white overflow tube. Hope this helps, Tom

Tom said it: most likely, it is flopper. Buy new one. Inspect it before you leave store. It should be flat and flexible. Buy exactly the same flopper as you have. Hint: take the old one with you to the store. This will save you trip or two...