Low water flow, leaks between the spout and handle or difficulty rotating the spout are all indicators that the cartridge in your single (or double) handle Moen brand faucet may need to be replaced.
Step 1: For low water flow issues, begin by cleaning out any dirt or debris from inside the faucet aerator. If this does not solve the problem or if low water flow was not the issue, go to your local hardware store or plumbing supply shop and purchase a Moen 1225/1200 replacement cartridge kit.
Step 2: Shut the water supply off to the faucet using the shut-off valves located beneath the faucet or the main water line shut off. Open the handles on the faucet to allow any water left in the line to escape and to ascertain the water is indeed shutoff.
Step 3: Depending on which Moen faucet you have, use a flat-head screwdriver to pry off the cover from the handle and use a Phillips head screwdriver to remove the faucet handle screw. Or use a hex wrench to loosen and remove the set screw from the front of the handle.
Step 4: Pull the faucet handle off and remove any washers or retaining rings from beneath the handle.
Step 5: Locate the brass retaining clip at the side of the cartridge stem and use a pair of pliers to remove the clip.
Step 6: Remove the white plastic square piece on the top of the new cartridge. Place this “tool” on the old cartridge stem, fitting the sides of the tool between the wings of the old cartridge stem.
Step 7: Grasp the white plastic tool with a pair of pliers and twist the old cartridge back and forth to loosen it from inside the faucet assembly.
Step 8: Remove the white plastic tool from the old cartridge and grasp the brass tip on the cartridge top with a pair of pliers. Pull the cartridge straight up and out of the faucet body.
Step 9: Align the new cartridge stem wings with the retaining clip notch and press the new cartridge into the facet body.
Step 10: Reattach the retaining clip.
Step 11: Re-install the faucet handle, reversing the steps previously followed.
Step 12: Turn the water supply on and test the new faucet for leaks before putting away your tools and calling it a day.