If you are getting hot water from the sink, then the problem is probably in the anti-scald setting on the shower handle. Pull the handle off the shower control, and you should see some kind of semi-circular piece with gear like teeth in it. This is ajustable so that you can only let so much hot water in so as not to scald the user. This is adjustable. Try repositioning it so that it allowes more hot water through the valve. There shoudl be a + OR - marking on it. Hope this helps.