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How to Install an Anti-Scald Shower Valve

This Old House plumbing and heating expert Richard Trethewey replaces a three-handle shower valve with a single-handle anti-scald valve

In this video, This Old House plumbing and heating expert Richard Trethewey replaces a three-handle shower valve with a single-handle anti-scald valve.


1. Turn off the water to the shower, then unscrew the three handles and escutcheon plates from the existing shower valve.

2. If the handles are rusted in place, free them with a handle puller.

3. Use a pipe wrench to loosen and remove the stem units from the hot-water valve, cold-water valve and diverter.

4. Hold the cover-plate template centered over the existing valve, then trace the template's outline onto the tiled shower wall.

5. Use a drill and ⅛-inch-diameter carbide-tipped masonry bit to bore six evenly spaced holes through the tile around the template's outline.

6. Cut the tile along the marked outline using an oscillating multi-tool fitted with a carbide-grit blade. Collect the dust with a wet/dry vacuum during cutting.

7. Chip the tile off the wall with a hammer and ½-inch cold chisel.

8. Cut out the old valve using a reciprocating saw with a metal-cutting blade.

9. Dry-assemble the copper pipe and fittings to join the new pressure-balance valve to the existing hot- and cold-water supply pipes.

10. Unscrew and remove the spindle from inside the new valve.

11. Disassemble the parts, apply flux to the copper pipe, fittings and valve, then reassemble the parts.

12. Next, spray water into the wall cavity with a plant mister to reduce the risk of starting a fire.

13. Solder the new valve to the water-supply pipes.

14. Reinstall the valve spindle that was removed in Step 10, then turn the water back on.

15. Test the valve by sliding on the handle and turning on both the hot and cold water. Remove the handle.

16. Roll a ball of plumber's putty between your hands to form a long ½-inch-diameter rope. Press the putty against the upper, rear section of the valve's cover plate.

17. Screw the cover plate to the shower wall centered over the valve. Scrape away any excess putty that squeezes out from behind the cover plate.

18. Set the escutcheon plate over the cover plate, then screw it partway onto the valve body.

19. Slip a rubber gasket behind the rear, upper section of the escutcheon plate. Finish tightening the screws.

20. Turn on the hot water, then use a thermometer to check the water temperature.

21. Use a screwdriver to adjust the temperature limit on the valve to ensure the hot water doesn't get any hotter than 120-degrees F.

22. Slip the cap assembly and handle onto the valve, then secure both with a single screw.

23. Cover the screw head with a push-on index button.

24. Buff the valve clean with a soft cotton cloth.