Locate and turn off the water shutoff valves to the faucet on which you are replacing the Moen 1225 cartridge.
Remove the faucet handle from the faucet. The handle removal depends on what type of faucet you are repairing. Most knob type handles have a cover plate on the center of the handle that you must pry off with a small flathead screwdriver. Removing the cover plate reveals the securing screw that you need to remove with a Phillips-head screwdriver to pull the handle off the faucet. Lever handles usually have a set screw on the side that require an Allen wrench for removal.
Take off the wall cover plate if you are repairing a bathtub Moen faucet. Two screws secure the plate to the wall that you must remove with a Phillips-head screwdriver.
Pull the washer and sleeve away from the Moen 1225 cartridge if your faucet has the sleeve covering the cartridge. Locate the c-clip that secures the cartridge to the faucet body. Pry the c-clip out with a small flathead screwdriver.
Find the cartridge removal tool in your replacement kit. Attach the tool to the top of the cartridge until the tabs lock over the cartridge. Turn the top of the tool with a pair of channel lock pliers to release the cartridge from the faucet body. Pull the cartridge out of the faucet body.
Insert the replacement Moen 1225 cartridge into the faucet body until the holes for the c-clip line up between the cartridge and faucet. Insert the c-clip into the faucet and cartridge, and push the clip in with your fingers until the clip locks in position.
Place the sleeve and washer over the faucet cartridge. Position the wall cover plate back on the wall if repairing a tub faucet. Secure the cover plate with the retaining screws.
Position the faucet handle back on the faucet, and secure with the retaining screw. Replace the cover if repairing a knob-type faucet. Turn on the water supply.