How to Convert a 3-Handle Shower Faucet to a Single-Handle Valve

Begin by shutting off the main water supply to your home to prevent any water flow. Open a faucet on a lower floor to drain any remaining water from the plumbing lines. Protect the shower or tub floor with old towels or a drop cloth. Gather all your tools, the new single-handle valve kit, and the remodel plate so they are readily accessible. Carefully review the instructions that came with your new valve, paying close attention to the required setback depth from the finished wall.

Start by removing the old faucet handles, which are typically held on by a set screw or a screw under a decorative cap. Unscrew the surrounding trim plates (escutcheons). To access the valve body, you will need to cut into the wall. Use an oscillating multi-tool with a grout removal blade or diamond tile blade to carefully cut the grout around the tiles you need to remove. Pry off the tile, then cut through the backer board to create an opening large enough to work on the plumbing. The opening should ideally be covered by the new remodel plate.

With the valve body fully exposed, identify the hot supply, cold supply, and the riser pipe going to the shower head. Use a compact tubing cutter to make clean cuts on the copper pipes, leaving enough pipe extending from the wall fittings for the new connections. You may need to use two pipe wrenches working in opposite directions to loosen any large threaded nuts holding the old valve body in place. Once all pipes are cut and connections are loosened, carefully maneuver the old three-valve assembly out of the wall cavity.

The new single-handle valve requires a solid mounting surface. Measure the distance between the wall studs inside the wall cavity. Cut a piece of 2x4 or 2x6 lumber to fit snugly between them. This is called a stringer or cross-brace. Position the stringer at the correct height for your new valve and secure it by driving deck screws through the studs into the ends of the stringer. After the brace is installed, use a deburring tool and emery cloth to clean the inside and outside of the cut copper pipe ends. This is crucial for creating a leak-proof seal with the new fittings.

Secure the new valve body to the wood brace using the provided mounting holes and screws. Now, reroute the plumbing. You will likely need short pieces of new 1/2-inch copper pipe and several push-to-connect fittings (like couplings and 90-degree elbows) to connect the existing hot, cold, and shower riser pipes to the new valve. Ensure the hot water line connects to the port marked 'H' and the cold water line connects to 'C'. Push the fittings firmly onto the cleaned pipes until they click or are fully seated according to the manufacturer's guide. If your valve has a tub spout outlet and you don't need it, make sure to cap it off as instructed. If you do have a tub spout, connect it now.

Before closing the wall, it is critical to test your work. Remove the faucet cartridge if required by the manufacturer for flushing, or leave it in if specified. Slowly turn the main water supply back on. Use a flashlight to meticulously inspect every new fitting and joint for any signs of dripping or seepage. Wrap a dry paper towel around each joint to reveal even the smallest leaks. Turn the valve on to pressurize the entire system, letting water flow through the shower head arm (cap it or attach the shower head). Turn the valve off and inspect all connections again. If a leak is found, turn off the water supply, relieve pressure, and remake the connection.

With the plumbing confirmed to be leak-free, you can now repair the wall. Cut a piece of cement backer board to fit the opening you created. Secure it to the studs and the wood brace using backer board screws. For a fully waterproof installation, apply a fiberglass mesh tape over the seams and cover them with a layer of thin-set mortar or apply a paint-on waterproofing membrane over the entire patch. Allow everything to cure completely according to the manufacturer's directions. This step provides the substrate for the remodel plate or new tile.

Once the wall repair is fully cured, you can install the final trim. First, slide the large remodel plate over the valve stem and center it to cover the old handle holes and your patch work. Next, slide the faucet's decorative escutcheon over the remodel plate and secure it to the valve. Install the valve cartridge if you removed it earlier. Attach the faucet handle, tightening it with its set screw using an Allen wrench. Wrap Teflon tape around the threads of the shower arm and tub spout pipe, then screw on the new shower head and tub spout. Apply a small bead of plumber's putty to the back of the tub spout flange before tightening it against the wall to create a seal.