Replacing moen 4600 valve

I contacted Moen directly with this same question and they let me know that they recommended a model 1225 replacement cartridge instead (that's what I get for trusting the guy at the hardware store to look up the matching part for me). Technically either one will work but apparently the plastic 1225 offers a tighter fit than the brass (and more expensive) 1220.

Moen also recommended cleaning out the inside of the valve with an old toothbrush or bottle brush and then flushing thoroughly before installing the new cartridge.

I will update this once I know if the new cartridge resolves my leak.

Update: After the installation of the model 1225 cartridge, the faucet works without any leaks from the stem. With the addition of a new knob the whole fixture is working better than new.

The moral of the story here is, when in doubt, try to contact the vendor (and post your results!)

It seems that Moen has an outstanding customer support, and after emailing them a couple pictures of my faucet to confirm the model they emailed me back instructions to replace the cartridge (along with a confirmation of the cartridge my model was using).

S o basically:

1. Turn water supply off
2. Use an allen wrench to remove the faucet's handle
3. Grab the collar and rotate counter-clockwise.
4. Using large pliers or channel locks remove the retainer counter-clock wise
5. Using pliers grab the white square of the cartridge and remove it from the faucet.

Documentation says that your bare hands should be enough for step #3. This was one of my problems I wasn't sure if I was going to need any tools. It seems that rotating should be enough and force can be applied.

To install the new cartridge you need to pay attention to the cartridge's 3 holes and 2 small tabs protruding. You need to look into the brass chamber to find the location of the 3 big and 2 smaller holes, align the cartridge and insert it making sure you are lining up the three big holes.

Gentle pressure should be able to rotate the cartridge.

After making sure that the cartridge is positioned correctly, you reassemble the faucet.