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1212 M-Core Cartridge 2 Series: 3 Port Valve

This article will give step-by-step instructions on how to replace a 1212 cartridge in a single handle M-Core valve shower.


  • The water supply shut off valves must be turned off- see article How To Turn Off The Water Supply To The Faucet.
  • Recommended Tools: Adjustable Wrench or Pliers, Needle-Nose Pliers, 3/32" Hex Wrench
  • We recommend covering the drain before beginning so to not lose any parts down the drain.

To View Complete Installation Video Visit: Installation Help at, Video Titled: M-Core 2-Series Cartridge Replacement

Handle Removal:


Using a 3/32" Hex Wrench, loosen the Handle Screw until you can remove the Handle.



Slide the Sleeve off of the assembly.

Parts Legend


6 Valve Body


5 Adapter with Check Valves


4 Pressure Balancing Puck


3 Cartridge


2 Cartridge Nut


1 Installation Sleeve (Included with 1212 Cartridge kit)

Cartridge Removal and Valve Body Preparation

disassembly step 1.gif

Unthread and remove the Cartridge Nut (2). Pull the gray Cartridge (3) out.

disassembly step 2.gif

Using Needle-Nose pliers, remove the Pressure Balancing Puck (4), O-Ring and Adapter (5).


Grease the Outer O-ring and inside of Valve Body (6).

Note: If you notice residue inside the Valve Body (6), see article Valve Body Cleaning and Flushing.

Re-Assembly: 3 Port Shower Only Valve (For 1212 M-Core Cartridge 2 Series: 4 Port Valve, Click Here)

3 port assembly step 1.gif

The 3 Port Valve will require removing the Pressure Balancing Puck (4) and Adapter (5) from the Installation Sleeve (1) and adjusting it. For more information, see next step.


Reinsert Pressure Balancing Puck (4) and Adapter (5) into Installation Sleeve (1) with the tab on the Adapter (5) up, aligning with the tab on the top of the Installation Sleeve(1).


3 port step 2.gif

Install the assembly into the Valve Body (6) aligning the adapter tab with the hole in the Valve Body.



3 port assembly step 2.2.gif



Align the 2 posts on Cartridge (3) to mating feature on Pressure Balancing Puck (4) and push Cartridge (3) into Valve Body (6) until it stops. Tighten Cartridge Nut (2) onto Valve Body (6) by turning it clockwise until hand tight, and then turn an additional 1/4 turn with a wrench.

For additional information on M-Core Shower products, visit Single Handle Shower: M-Core at

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