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Shower Faucet: Leaking-M-Core Valve

The most common reason for a leaking shower is the cartridge. The full M-Core line includes two series of valve assemblies, each using a different flow cartridge. See the chart below for troubleshooting help.

Symptom Solution  

Continuous Leaking with the Handle in the Off Position

Water Leaks From Handle

Water Leaks Around the Escutcheon/Back Plate 

New Installation

  • Tighten the cartridge nut-Confirm the cartridge and system have enough compression. Installation should be hand tight plus one quarter turn with a wrench.
  • Confirm that the cartridge parts are in place and correctly assembled. Following the instructions in the article M-Core Cartridge Basics, verify that all parts are present, no seals are damaged or missing and the cartridge assembly is reinstalled in the correct order. 
  • Replace the flow cartridge. The cartridge number is based on the M-Core Valve series, See Identify the Valve Series and Cartridge Below.

Existing Installation:

Water Leaks Behind the Wall Call us at 1-800-289-6636 or Contact Us

Showerhead Leaks When Running the Tub Spout Only

This symptom is called Stacking, see article What is a Stacking Leak?

Identify the Valve Series and Cartridge:

2 SERIES- A 2 Series M-Core valve handle rotates only to adjust the water temperature, the system only provides one level of water pressure. The 2 Series uses the 1212 flow cartridge.

3 SERIES-A 3 Series M-Core valve handle rotates to adjust the water temperature and pushes in and out to adjust the force or volume exiting the showerhead or tub spout. The 3 Series uses the 1213 flow cartridge.


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

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