Step 5 · Prepare and Install New Cartridge

This is the step people usually slow down on. Go finger-tight first, then a quarter turn. No rush — replay the clip whenever it helps.

Before inserting the new cartridge, inspect the inside of the brass valve body. Use a cloth or a small nylon brush to clean out any sediment, mineral deposits, or pieces of old rubber O-ring. Take the new cartridge and apply a thin layer of plumber's grease to all of its rubber O-rings. This lubricates them, making installation easier and helping to create a perfect seal. Align the new cartridge correctly. Look for the 'H' marking on the side of the cartridge and make sure it aligns with the hot water inlet on the valve body (typically the left side). Carefully push the cartridge straight into the valve until it sits flush and is fully seated.