A little while back, I was experiencing signs of a worn out valve in my main floor tub/shower. The knob was getting difficult to turn and soon I started noticing evidence of a small leak that was damaging the ceiling of the basement below the valve.
I opened up as much of the plumbing as I could get to through the access panels and confirmed that the valve, not the pipes were leaking. It turns out that the Moen shower valve in the main floor bath uses an easily replacable cartridge insert. In about an hour, including a trip to the neighborhood hardware store for a new cartridge, my shower valve was repaired and working better than ever.
Here’s how it was done:
Start by turning off the water supply to the tub. Pry the decorative cover from the end of the knob with a straight screwdriver, then unscrew the knob and remove it. With the knob gone, it should now be possible to remove the large trim ring against the wall by pulling a couple more screws.
Using a small pliars, pull out the small retaining clip protruding from a slot in the valve body near where the knob attaches. (As an aside, check out the weird blue fiberboard on the back side of the wall. It was soaking up the leaking water like a sponge. I don’t believe this is a code-compliant building material for a wet area…)
Once the clip is removed, reattach the knob and pull straight out until you have removed the valve cartridge.
Then remove the knob from the old cartridge, attach the knob to the new cartridge, and reverse the removal steps to finish the installation.
Before reinstalling the trim ring, I replaced the gasket around the edge because the old one was worn out. Adhesive foam weatherstripping was just the right thing for the job.
With the new cartridge, the tub and shower valve work like new. I finished this repair six months ago and I’ve had no evidence of leaks or trouble throughout that time.