How to Replace a Clogged Shower Valve

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.

Inside the wall behind the handle and escutcheon plate sits the valve body, with a hot pipe on one side and a cold pipe on the other. The key component is the cartridge — it controls the mixing of hot and cold water and contains a pressure-balancing mechanism. A retainer clip holds the cartridge in place; once removed, the cartridge pulls straight out, revealing the hot and cold ports where sediment buildup is most likely to restrict flow.

On a recent This Old House project, a homeowner reported that whenever someone turned on the hot water in the kitchen or ran the dishwasher, the shower would lose hot water completely and take a long time to recover. The culprit turned out to be the shower valve’s internal cartridge — a common issue that a simple cartridge replacement can resolve without the need for a costly full valve tearout.

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.

From a This Old House Project: When Richard Trethewey helped homeowner Nick replace a clogged shower cartridge, he offered one extra piece of advice that will save future headaches: greasing the O-rings on the new cartridge with waterproof grease now makes it far easier to remove the next time it needs replacing. As Richard told Nick: “I actually make it easier for you when you have to change this 15 years from now.” Once the new cartridge was in and the water restored, they confirmed proper operation by checking that the handle moved smoothly from cold all the way to hot with strong pressure.

Why it matters: The cartridge has been seated in the valve body for years, and the O-ring seal can crust up over time. If you simply try to pull it out with pliers, you risk breaking it and leaving parts inside the wall — which could mean replacing the entire shower valve. A special cartridge-puller tool with shoulders that match the cartridge can help you twist and break that seal before pulling it free.

Tools: