Sometimes a rebuild of the internal components of your shower valve is not enough to fix a leak. In older faucets the metal will corrode causing cartridges, seats and other components to not seal properly. Here in Albuquerque and Rio Rancho our ground water is very hard. These minerals in the water seize up the components in the fixtures fixtures causing them fail. The hard water damage can clog up the fixture so much that its impossible to remove components with out breaking the faucet its self.
In this case the entire faucet will have to be removed and replaced.
When a plumber needs to replace the faucet he first has to get access to it inside the wall. This usually involves (preferably) cutting out a square of drywall behind the shower valve. Sometimes if there is no drywall access tile will need to be taken out.
Once the drywall or tile is removed the old faucet must be cut out of the wall. The faucet is usually strapped and secured inside the wall to a stud. Straps are removed and usually some of the stud needs to be cut out. Hot and cold lines to the faucet as well as tub spout and shower lines will need to be cut. Any handles and trim on the front of the faucet are removed and the faucet is now ready to be removed from the wall.
The new tub valve body can now be installed inside the wall. Hot, cold, tub and shower lines are reconnected and the tub valve is secured inside the wall. Handles and trim are installed and the new shower valve is ready for use.