In this video, This Old House plumbing and heating expert Richard Trethewey solves the mystery of hot water from the cold-water faucet.
- Turn off the water to the bathroom, then unscrew and remove the handle and finish trim from the shower valve.
- Unscrew and remove the single-lever cartridge from the shower valve.
- Reach into the valve with needle-nose pliers and pull out the secondary cartridge.
- Pull apart the secondary cartridge, separating the control head from the pressure balancer.
- Unscrew the pressure balancer and inspect the interior diaphragm. If damaged, replace the old pressure balancer with a new one.
- Reassemble the shower valve by reinstalling the cartridges.
- Turn the water back on and test the operation of the shower valve. Reattach the finish trim and handle to the valve.
- Test the water at a nearby sink to ensure the hot- and cold-water faucets are operating properly.