A spout leak, difficulty controlling the temperature and loss of water pressure are all signs that the cartridge in your Moen faucet may need replacing. Because cartridges are, in principle, easy to remove, you should be able to do the job in under an hour. It can take more time and effort, however, if the cartridge is stuck, which isn't unusual. That's why it's a good idea -- if you have a Moen faucet -- to have a Moen cartridge puller, because it's the most effective tool for extracting stuck cartridges.
Turn off the water to the faucet before you replace the cartridge. Use the shut off valves under the sink or, if you're working on a tub or shower faucet, turn off the main water supply for the house.
Remove the faucet handle or handles. Even if you have a double-handled model, only one of the cartridges may need servicing. The handle is either held by a screw that you loosen with a Phillips screwdriver or a hex nut that you loosen with an 1/8-inch hex wrench.
Pull out the cartridge retaining pin with needle-nose pliers. Some faucets have a temperature limiter that you have to remove before you can get to the pin. You can usually pull off the limiter with your fingers.T here may also be a metal sleeve around the valve. You should be able to pull this out with the pliers.
Grasp the valve stem with pliers and pull it straight out of the valve housing. If the faucet isn't too old and you don't have hard water, it should come right out. Mineral deposits can make it stick, however, as can the O-ring around the cartridge, which fuses to the housing over time. If the cartridge is stuck, pull it out with a cartridge puller.
Insert the puller over the cartridge and screw the central screw into the cartridge stem. Turn the handle of the puller clockwise to unfreeze the cartridge, then pull the cartridge out. You can also continue turning the handle to back the cartridge out gradually.
Grease the O-rings of the replacement cartridge with plumber's grease, then insert the cartridge, being careful to align the marks on the cartridge with the corresponding ones on the valve housing. Look up the model on Moen's website for installation instructions if the alignment isn't obvious.
Push the retaining pin back into the proper holes when the cartridge is fully seated. Replace the metal sleeve and temperature limiter. Screw on the handle and turn the water back on.