You description makes sense. You have an access panel in the closet so that you don't have to cut tile to replace the valve. This is a good thing. If it is a single handle valve, you probably need a cartridge for the valve, which can be replaced from the front by removing the trim or cover plate. If it is just the hot water that runs on a two handle shower, it could be the hot water stem that needs to be replaced in the hot side valve and not the entire valve. it's easy to buy stems for ...»