How to Repair a Shower Anti-Scald Pressure Balancer

In this video, This Old House plumbing and heating expert Richard Trethewey solves the mystery of hot water from the cold-water faucet.

Steps:

1. Turn off the water to the bathroom, then unscrew and remove the handle and finish trim from the shower valve.
2. Unscrew and remove the single-lever cartridge from the shower valve.
3. Reach into the valve with needle-nose pliers and pull out the secondary cartridge.
4. Pull apart the secondary cartridge, separating the control head from the pressure balancer.
5. Unscrew the pressure balancer and inspect the interior diaphragm. If damaged, replace the old pressure balancer with a new one.
6. Reassemble the shower valve by reinstalling the cartridges.
7. Turn the water back on and test the operation of the shower valve. Reattach the finish trim and handle to the valve.
8. Test the water at a nearby sink to ensure the hot- and cold-water faucets are operating properly.