A thermostatic shower valve blends hot water with cold water to ensure a constant and safe temperature while preventing scalding. Installing this fixture is a challenging feat that a home DIYer can accomplish with time, patience and some knowledge of carpentry and bathroom plumbing.
Connect and flush the waterlines. Fasten the valve to the hot and cold supply lines with a pipe wrench.
Stop the showerhead waterline, and slice a piece of 1.2 cm (1/2 inch) PVC pipe, with pipe cutters, to the length needed for the shower head. Apply PVC glue inside the trod adaptor and along the end of the waterline, then push the adaptor onto the end of the pipe. Tighten the waterline to the shower head and the outlet for the shower valve to properly secure them.
Install the drop-ear elbow, and attach one of the 36.2 cm (14 1/2 inch) 5 by 10 cm (2 by 4 inch) boards behind the showerhead supply line. Use dry wall screws to fasten the top with the wide side facing forward. Then, apply PVC glue inside the drop-ear elbow and at the end of the showerhead waterline. Push the drop-ear elbow onto the pipe, with the threads of the elbow facing forward, and use wood screws to secure it to the 5 by 10 cm (2 by 4 inch) board.
Mark the cavity's top and bottom pieces, and place the remaining 36.2 cm (14 1/2 inch) 5 by 10 cm (2 by 4 inch) boards on a worktable with one side facing up. Then, measure the end of one piece and mark it at 17.1 cm 19 cm (6 7/8 and 7 5/8 inches). After, measure the ends of the remaining piece and place marks at 9.6, 11.5, 27.1 and 24 cm (3 7/8, 4 5/8, 10 7/8 and 11 5/8 inches). Put the combination square on the measured marks and draw lines across each of the pieces.
Cut notches for the waterlines. To do so, place marks on the lines that are 4.3 cm (1 3/4 inches) from one long side of the lumber, then draw a 1.8 cm (3/4 inch) line connecting the marks on the lines that are 1.8 cm (3/4 inches) apart. Cut along the lines with a band saw while wearing proper safety equipment to avoid injury.
Construct the cavity box. Place the timber on the worktable so the narrow edge without the cutouts is facing up, and set the 20 cm (8 inch) 5 by 10 cm (2 by 4 inch) boards between them (with one narrow side also facing up). Then, put them on the outside of the cutouts for the hot and cold waterlines, and use plasterboard screws to secure.
Check the connections, and firmly screw the PVC plug into the drop-ear elbow. Turn on the water to check for leaks. If needed, fix the leaks by fastening the joints more tightly or with appropriate caulking.
Install the cavity by fastening the box, with plasterboard screws, between the studs so the cutouts properly fit around the waterlines. Install the wall covering, but leave an opening for the cavity box. One of the main features of a thermostatic shower valve is its ability to shut down if the cold water is interrupted. Therefore, a cavity box must be installed in the wall around the shower valve for future access. The shower valve comes with a cover plate that fits over the box and around that shower valve, and is easily removed for prompt access. Also, calibrate the temperature settings if desired.