First, look for shut-off valves underneath a nearby sink or behind an access panel for the shower. If you cannot locate individual shower valves, you will need to turn off the main water supply to your entire house, usually found in your basement, utility closet, or near your water meter. Always confirm the water is off by testing a fixture before proceeding.

While pliers can sometimes work for removing a cartridge, a specialized cartridge puller is highly recommended, especially for older or stubborn cartridges. Using the correct puller minimizes the risk of damaging the faucet body or the new cartridge during installation, saving you potential frustration and costly repairs. It's a worthwhile investment for this DIY project.

The most reliable way to get the correct replacement cartridge is to remove the old one first and take it to the hardware store for a direct match. If that's not possible, try to identify the faucet brand and model number, often found on the escutcheon plate or handle, and look up the compatible cartridge online or in the store's parts catalog. Faucet manufacturers have distinct cartridge designs.

If the leak persists, first re-check that the new cartridge is seated correctly and all components are tightened snugly but not over-tightened. Ensure no debris or old O-rings were left inside the faucet body preventing a proper seal. In rare cases, the faucet body itself might be damaged or corroded, requiring a more extensive repair or replacement.