How to change out a Moen shower cartridge?

To change out a Moen shower cartridge, you need to first identify your model and shut off water to prevent flooding. Start by turning off water to the shower. Look for shutoff valves in the basement, access panel behind the shower, or shut off the main house water if needed. Open the shower handle to release pressure and confirm water is off. Remove the handle. Most Moen handles have a small cap that hides a screw, or an Allen screw underneath. Unscrew and pull the handle off. Remove the escutcheon plate and any sleeve. You will now see the cartridge held in by a brass or plastic retainer clip. Pull that clip straight up with pliers. This is critical, do not lose it. Now extract the old cartridge. For Moen 1200 or 1225 cartridges, you can often pull straight out with pliers. For Moen 1222 Posi-Temp cartridges, you will likely need the Moen cartridge puller tool that comes with the new cartridge or can be bought separately, as they get stuck from mineral buildup. Twist slightly as you pull. Note the orientation of the old cartridge. Clean inside the valve body with a cloth. Apply silicone grease to the new cartridge O-rings, align it correctly with the H and C markings, push it in fully, reinstall the retainer clip, and reassemble the trim. Turn water back on and test for leaks and proper temperature control.