Randy, take the handle and trim plate off the shower valve.replace just the handle and turn the shower on.If water is coming from the push button diverter, replace it. this part screws into the valve. if the water is coming from the shower head area, reseal or replace the shower arm. as far as your other questions. the valve is 14 years old! It is time to replace some parts!! if you are lucky you can reuse tile, trying to take it off the wall will cause it to break.