Step 3 · Access the In-Wall Plumbing
To replace the valve, you must create an opening in the wall. Use a stud finder to locate the studs on either side of the plumbing. Mark out a rectangular area large enough to comfortably work in and to fit the new valve body, typically about 12 inches wide by 10 inches high. Put on safety glasses and a dust mask. Use an angle grinder with a diamond blade to carefully cut through the tile along your marked lines. Then, switch to an oscillating multi-tool with a plunge-cut blade to cut through the cement backer board behind the tile. Carefully pry off and remove the cut section of tile and backer board to expose the old valve assembly and pipes.