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Moen Solutions

B17-Troubleshooting Shower Stacking




Symptom: When a 1, 2 or 3 handle tub and shower exhibits the annoying symptom of shared flow or STACKING.  The consumer turns the water flow on and instead of the flow immediately coming out off the tub spout, they are getting a trickle or more out of the showerhead,

This document cover the diagnosis process for a one-handle, two-handle or three handle tub and shower faucet.  if none of the reasons below apply please contact us for further assistance at 1-800-BUY-MOEN.

Stacking Checklist

1. Installation Layout:  Check that the spacing between the main valve and the outlets for the tub spout and showerhead are within the guidelines on the instructions.clipboard_e82c0b525eab5892fb7e5a3b414f1e854.png


  • The tub spout must be installed 6" min and 9" Max below the valve
  • The showerhead must be at least 46" above the valve.

Solution:  Re-plumb the outlets to the correct spacing.


2. Piping Material:  The installation instructions specify that the piping used from the Valve Down to the Tub Spout outlet be 1/2" metal pipe (Copper, Galvanized, Brass IPS (Threaded) pipe.

Solution: Replace incorrect piping. clipboard_e31ef63b8976774b2be764184a83bbb05.png


Pex, Braided Flexible Water Supply Lines and CPVC all have small interior diameters which create the back up of water in the system that can result in the STACKING symptom




3. Tub Spout:  Remove the tub spout.  If the stacking problem goes away, examine the tub spout for restrictions or damages, this could include debris or the white diverter gate in the spout is not opening or closing completely.

Solution: Clean the restriction and insure the diverter is pushed all of the way down.  If necessary, contact Moen for a replacement tub spout.  clipboard_e6d66d0303459cce10757515e98689aaa.png


4. Multiple elbows between the valve and tub spout:  Only one elbow should be used between the valve and spout.  Elbows slow the water down as it exists the spout and could  create the stacking symptom.

Solution:  Remove any additional elbows to leave on elbow between the valve and tub spout.  clipboard_edc10c344144f7bf9142f4cc74695722c.png



   5. Upside-down valve:  If a valve is installed upside down it will send the water to the showerhead first instead od down to the spout.  Check you installation to make sure "UP" is facing the ceiling.

Solution:  Reinstallation of the valve may be required to correct stacking.  clipboard_e17e38c0a1e793133d4a68b612712cfa6.png

Two- handle Tub and Shower Diagnosis


1. Upside-down flow director:  If the valve was mounted upside-down to accommodate water supplies that come in from the ceiling, the flow director must be removed and installed into the side of the valve the water supply enter.

For valve mounted upside-down to accommodates supplies from the ceiling  clipboard_ef65872ff48464befc2cd621999483a45.png


Supply ports on bottom


Unscrew the Flow director




Supply ports are now on top


Flow director installed threaded side on top



If you are not able to correct the issue creating the Stacking, consider installing a SHOWER ARM VOLUME CONTROL- Moen part 91888.  This device will allow you to shut the water flow off a the showerhead,  It is Not designed to be used a substitution for the control handle and should never be used as your main on/off control.