Moen’s products have proved to me to be long-lasting and relatively simple to install or repair.  Below I have outlined the symptoms of a faulty single-handle shower control, the cost, method and instructions for repairing it, to save you a significant amount of money and trouble compared (or contrasted) with what a plumber would charge you in parts and labor to do the same thing.  Terms like “splash guard” instead of “escutcheon,” and “key” instead of “retainer clip” describing parts are used because they are, in this writer’s view, functionally descriptive.  This is by no means a unique article, but I thought it might be helpful to some DIY non-plumbers.

We had recently replaced a water heater, and it was quite corroded.  After the new water heater was installed, we noticed that the temperature adjustment in both our Moen shower controls had now become difficult to control.  In the position we would normally turn the handle to receive a nice, hot shower, it was cold.  If we turned the now-stiff-control just a small degree, the water would suddenly come through too hot.  Try to turn it back where it was to even it out, and it would become even colder again. 

Oddly, although it may have become too hot at one point, turning it further to the left would yield cooler water, and turned all the way to the left would not be as hot as it should be.  One check I performed was to try the nearby sink faucet; it adjusted properly, providing higher-temperature water than the shower control.  We then knew our water heater was not at fault; we were getting 120-degree hot water there (measured with a candy or deep-fry thermometer).  I noticed that the controls had become stiff to pull out or push back in.  With a bit of research I found that the cartridge might need changing, although no leaks were present.  Many times cartridges are replaced because of leaking.  This experience gave me some leading indicators of shower control cartridge failure.  

If your shower control used to be easy to adjust but recently has become stiff to operate, or your hot/cold temperature control does not provide consistent, continuous temperature change from cold to hot as it used to give, or setting the water temperature has become a tricky operation, where small turns may produce either freezing or scalding hot water, your shower control cartridge may need replacing (and soon!).  As it turns out, mineral deposits and corrosion are generally the culprits.  

Moen uses either a 1225B plastic cartridge which normally sells for around $20 at a major DIY store (but one may find lower prices on the internet), or a 1200 brass cartridge which sells for around $22.  You may pay more at a plumber’s supply but they normally will give you more information about the products they sell you.  After you learn, you can buy at places like major DIY warehouses which are less expensive, but generally don’t always have the most knowledgeable salespeople, since they are discount parts suppliers (although a few may prove to be quite informative).   The plastic cartridge is extremely easy to adjust and is cheaper than the brass, which gives a more solid feel (slight continuous resistance) to the shower adjustment.  I repaired the guest bathroom shower control using the plastic and brass Moen 1225B cartridge, and the master bath with the Moen brass 1200.  

The instructions that come with the cartridges are in the universal language of pictures; very small, but step-by-step nonetheless.  Find photos below for every step of the repair process. 

1. Purchase Moen Cartridge 1200 Brass or 1225B Plastic and Brass at DIY home improvement warehouse or on internet. 

2. Shut off water supply to shower or house.  (If you don’t have a local shutoff control, there are the main and secondary shutoff valves for your house generally located near the street.  Call your local water department if you are unsure.  Many localities frown on your using the primary or curb-side shutoff.  The secondary is usually found nearby the main under a green lid.  A little gentle digging may be necessary to find the valve.  You also may need to find or purchase a knob with an adapter to turn the valve off.) 

1. Moen 1225B Single Handle Plastic and Brass Cartridge

3.  Remove brand-name cap

4. Attachment Screw Beneath Brand Cover

 4. Notice attachment screw, probably phillip’s

5. Remove Attachment Screw w Phillips's Head Screwdriver

6. Splash Plate with Cartridge inside Cartridge Cover

7. Remove Splash Plate Screws with Phillip's Head Screwdriver

8. Pry Loose Splash Plate

9. Cartridge inside Cartridge Cover

10. Slide Cartridge Cover off to Remove

11. Find Key Above Cartridge's Top Center

12. Remove Key with Vise-Grips or Pliers

14. Pull Cartridge Straight out with Pliers/Vise-Grips

 Take note of how the old cartridge looks and at what orientation it was installed.  To set the cartridge in place, push it straight in, fitting it in the same way (depth and angle) as the old cartridge was.   It should look like the picture above.   Likely, your old cartridge appears badly corroded and the washers are flattened and stiff.  The new cartridge may even turn without the handle, so set the control end horizontally, and perform the install in the reverse order as the removal.