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Have you ever seen water run or drip from the shower while you're trying to fill the tub? Plumbers call this "stacking." Pressure balance valves with high flow rates, such as the Grohsafe 35 015 or single function pressure balance GrohFlex, sometimes have "stacking" occur when installed incorrectly.
If this happens on a job, the plumber has one (or more!) of the following problems (listed in order of likelihood):
- Excess water pressure (in excess of code mandated 80psi).
- The valve is installed upside-down (water needs to be directed to the diverter tub spout first). See diagram.
- Shower head or hand shower outlet is too low (it should be at 6 feet from floor, minimum. When using a hand shower, the riser should run to 6 feet+ and make a "U-turn" back to the chosen outlet height).
- Low-flow diverter spout (that is, the diverter spout is restricted - either with debris, or by design - and won't allow the full flow of water from the valve out the spout. All Grohe diverter tub spouts are full flow).
- Reduced diameter piping on tub outlet. (The installation instructions call for 1/2" piping, but 1/2" PEX fittings often have a reduced inside diameter, reducing the amount of water that can flow.)
- Cartridge o-ring failed. (The 35 015 Grohsafe introduced an o-ring on the cartridge to separate the tub outlet near the front from the shower outlet at the rear of the valve. If this o-ring was torn during installation at the factory, water can go out both outlets.) I have seen this once since 2009.
The plumber calls to say "I have installed a Grohe 35 015 pressure balance valve, and no matter the temperature selected, water is running from the shower! What is wrong, and how can we fix it?" You ask the plumber the following questions:
- "What is the incoming water pressure?" He answers, "60psi."
- "Pull the cartridge, and look into the valve body - are two outlets pointing down to the tub or up to the shower?" He answers, "Up to the shower."
- "Is there a shower head or hand shower? How high is it installed?" He answers, "Shower head at 6 feet."
- "What brand is the diverter spout?" He answers, "Grohe."
- "What is the piping on the tub outlet?" He answers, "Copper pipe."
Apply what you learned: What did the plumber do wrong to cause the water to stack and drip out of the shower?