Step 9 · Install New Cartridge
Take the new cartridge. If you have plumber's grease, apply a light coat to the rubber O-rings to help it slide in easily and prevent tearing the seals. Align the cartridge correctly; there are typically tabs or notches on the side of the cartridge that must fit into corresponding slots inside the faucet body. For a Moen 1225 cartridge, the 'H C' marking should be facing up. Push the cartridge firmly and evenly down into the valve body until it is fully seated.