American Standard single lever shower faucet won't turn to the left (which is supposed to be hotter but it appears to be set up backwards and is the cold side). can barely stand to take a shower because it is so hot and the lever will not turn left at all past center. I have removed the handle and see what appears to be the problem. there is a red ring with stops on it that is preventing movement to the left. I'm sure this is (hopefully) an easy fix but am afraid to proceed with out knowing exactly what to do. I don't want to make it worse. help for the non-plumber?