Shower Valve Service Lessons

The author goes through tips on servicing a Moen Posi-Temp valve

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Moen is one of the most common valve manufacturers in the industry. Here I take a look at servicing Moen’s Posi-Temp tub and shower valve.

Removing the Cartridge

The first step is some area preparation. Put a rag over the tub drain so that small parts don’t fall in. Place another clean rag nearby to set the parts on as they come out. Make sure you set the parts down in the same order that they come out in order to limit confusion on the rebuild. This specific valve is easy to repair, but it is a good practice to do consistently, especially in cases of ancient valve setups.

Once you have prepped your work area, take the index button or “knob insert” out with a pen knife, being careful not to break it. Next, remove the handle screw and the handle. For the Posi-Temp family Moen makes an acrylic type handle, a brass lever handle with a forward-facing index button, and a third handle that is a brass lever handle with a downward-facing screw holding the handle into a plastic handle adapter. Once removed, you need to remove the handle screw that holds the handle adapter.

Just behind the handle is a brass washer. There is always confusion among plumbers on where exactly this washer is placed since it has likely been re-installed incorrectly a few times on previous repairs/installations. It fits right behind the handle. 

Next, pull straight out to remove the temperature limit stop, key stop and stop tube. The first two are white plastic, one with male ridges and the other with receiving female ridges that have offset stop bumpers to only allow the handle to reach a certain point on the hot side, which is why it is considered anti-scald.

Now shut the water off to the unit. Moen makes these shower valves with or without integral stops, with 90-degree turn on/off, and with screwdriver stops in which you completely screw in the stop to shut off the water supply. The 90-degree turn stop and the screw stop look identical and should be tested and verified that the unit is off before proceeding.

The only two parts remaining are the retainer clip and the cartridge. This is where servicing this valve can get tricky. The retainer clip has to come out first. It has a hole in the top and pulls straight up and out. There is usually not a lot of room and sometimes they can be a chore to get up and out. If it is difficult to remove, try gently prying with a scratch awl or a small Allen key. Make sure and hang onto it with a pair of needle nose pliers because it will let go all at once and will usually fall behind the shower wall lost forever. If the clip was difficult to remove, replace the clip or sand any areas that look calcified on both the valve body slot and the clip. 

Next is the pulling of the cartridge. Make sure to get a good Moen cartridge puller. Without one, you will have a very difficult time pulling some cartridges — especially “frozen” ones. The puller features side slots that fit into either side of the cartridge, a screw that screws into the handle screw receiver, and a nut to tighten down with a wrench once the tool is assembled to help get the cartridge loose. Once you free the frozen cartridge, wiggle and pull straight out. It is a good idea to have a small piece of plastic sheet or a rag at the ready when the cartridge is removed as a small amount of water will drain as it comes out.

Re-Installing a New Cartridge

The benefit of the Posi-Temp cartridge is that the hot and cold are marked on the cartridge. Grease up the cartridge rubbers with plumber grease and slide the cartridge into the housing, orienting the hot and cold correctly. Push the cartridge all the way in until it stops, hold it there tightly and install the retaining clip. Grease the retainer clip as well as every other screw and part that gets re-installed. Now grease the inside of the slip tube and continue to reassemble the unit making sure to keep the same setting for the scald guard setting. 

Grease and re-install the trim kit and handle assembly. Finally, test the operation. Prevent a callback by using an infrared thermometer and checking the water temperature setting. Many times a homeowner will complain that you changed the temperature. Show the homeowner how hot it was when you started and how hot it was when you left. Mark this information on the invoice that the customer signs before you leave. Remember — it didn’t happen if it wasn’t written down.

About the Author

Anthony Pacilla is a registered master plumber for McVehil Plumbing in Washington, Pennsylvania. He has 22 years of experience in the plumbing and HVAC trades, and has a bachelor’s in business and economics from Thiel College. 



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