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

Begin by shutting off the main water supply to your entire house. Open the hot and cold handles on the existing shower faucet, as well as another faucet at a lower level in the house, to drain as much water as possible from the pipes. Place a bucket under the shower spout to catch any residual water. Lay down an old blanket or drop cloth in the tub or shower base to protect the surface from scratches from dropped tools or parts.

Go to the wall directly behind the shower valve. Use a stud finder to locate the studs on either side of the plumbing pipes. Mark a rectangle for your access panel, typically about 12-16 inches wide and tall enough to give you ample room to work. Use a level to ensure your lines are straight. Carefully cut along the marked lines using a drywall saw. Remove the cut piece of drywall and set it aside; you can reuse it to patch the hole later.

From the front side of the shower, remove the three faucet handles. They are typically held on by a small set screw, which may be hidden under a decorative cap. Pry off the caps with a small flathead screwdriver and loosen the screws. If the handles are stuck, use a specialized handle puller tool. Once the handles are off, unscrew the surrounding decorative plates, called escutcheons, to expose the valve stems.

Working from your access panel, identify the hot and cold supply lines and the pipes leading to the shower head and tub spout. Using a tubing cutter, cut the hot and cold pipes below the old valve body, and cut the shower riser and tub spout pipes above and below the valve assembly. Be prepared for some water to spill out. Once all four pipes are cut, the old three-handle valve assembly should be loose and can be removed from the wall cavity. Wear safety glasses during this step.

Consult the new valve's instructions for the correct installation depth. This is crucial and is measured from the front of the valve to the face of the finished wall (tile or shower surround). Install a new piece of 2x4 lumber horizontally between the wall studs to serve as a secure mounting bracket for the new valve. Measure and cut the existing pipes as needed to align with the new valve's ports. Clean the outside of all pipe ends and the inside of your new fittings using a pipe cleaning brush and sand cloth until they are shiny and free of oxidation.

Disassemble the new valve, removing the plastic cartridge to prevent heat damage during soldering. Apply a thin, even layer of flux to all cleaned pipe ends and fittings. Assemble the pipes and fittings onto the new valve body, ensuring the 'UP' or 'SHOWER' port faces up. Position your heat shield to protect the wood framing. Heat the joint with the propane torch, moving the flame constantly. Once hot enough, touch the lead-free solder to the joint opposite the flame; the solder should be drawn into the joint by capillary action. Repeat for all four connections: hot in, cold in, shower out, and tub spout out. Allow the joints to cool completely without being disturbed.

Once the solder joints have completely cooled, reinstall the valve cartridge according to the manufacturer's directions. Place a rag or small bucket inside the wall under the valve. Go to the main water shutoff and turn it on SLOWLY. Listen for the sound of pipes filling. Return to the access panel and meticulously inspect every solder joint for any drips or beads of water. If you find a leak, you will need to shut off the water, drain the system, and re-solder the faulty joint. Also, test the valve function by turning the handle to run water to the tub spout and shower head.

After confirming there are no leaks, you can repair the access wall. Re-insert the piece of drywall you cut out earlier. Secure it by screwing it to the studs or by adding small wood backing strips for support if it's not between studs. Apply drywall tape over the seams, then spread a thin layer of joint compound over the tape with a putty knife. Allow it to dry completely as per the manufacturer's instructions. Apply two to three more coats, sanding lightly between each coat, until the patch is smooth and flush with the surrounding wall. Prime and paint to match.

Now for the final step. Slide the new, large escutcheon plate over the valve, which will cover the old handle holes. Secure it to the wall or valve body as per the instructions. Install the new handle, usually by sliding it on and tightening a small set screw with an Allen wrench. Wrap the threads of the shower arm with Teflon tape and screw on the new shower head. For the tub spout, apply plumber's putty to the back edge if it's a slip-on type, or Teflon tape to the threads if it's a screw-on type, and install it. Remove the protective film from the new trim and enjoy your new shower.