In this video, This Old House plumbing and heating expert Richard Trethewey replaces a clogged shower valve that would not allow hot water into the shower.
Steps for replacing a clogged shower valve:
1. Cover the tub drain with a rag to prevent any dropped parts from falling into the drain.
2. Unscrew and remove the handle and escutcheon plate from the shower valve.
3. Close the hot- and cold-water shutoff valves to the shower.
4. Use a pocketknife to carefully pry the retainer clip from the shower valve.
5. Hold a plastic shield beneath the valve to catch any water, then use pliers to pull out the old shower cartridge.
6. Smear waterproof grease onto the O-rings of a new shower-valve cartridge.
7. Push the new cartridge into the shower valve, making sure you correctly orient the hot- and cold-water indicators.
8. Press the retainer clip onto the valve to secure the cartridge.
9. Open the hot- and cold-water shutoff valves.
10. Reinstall the escutcheon plate and handle.