problems with Grohe shower mixing valve

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the_eleven

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Greetings! First post for me here.

After 17 years a client's Grohe 34-126 shower mixing valve started only delivering water between hot and warm temperatures. I am a general contractor with plumbing experience, from rough and finish install to servicing installed fixtures.

I ordered a new thermostatic cartridge, part # 47662000, and a set of non-return valves, part # 1411600M directly from Grohe.

These new parts were installed, water turned back on, and unfortunately the problem remains.

I have construction photos at rough-in and verified that the valve is fed with hot on left, and cold on right. The cold side flows strongly from the lavy sink and adjacent soaking tub in this bathroom, as well as interconnected sink in the laundry room on the other side of the wall.

If I shut off hot at the valve (with the 8mm hex nut) there is no water flow at the spout. If I shut off the cold, there is water flow.

I am totally stumped here. Can anyone educate me on what may be happening? Should not there by cold output from these valves, in case someone needs a cold shower? ;-)

Thanks in advance for any help with this!
 

TJRAD

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Hello The eleven,
let me ask you a couple of questions. when you installed the cartridge did you calibrate it to 100 degrees?
second question, does the client have a tankless water heater or standard?
I will stand by for your response.
 

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Breplum

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Check for cross flow at the water heater by shutting off the cold supply, then open any hot water tap...after depressurizing, there should be no hot flow whatsoever. If there is flow still, that means a cross connection, or if you have a Navien tankless, the check valve has failed. If you have hot water recirculation that could be a source of cross failure. Kohler shower valves elsewhere in the house are also notorious for cross connection internal failures.
 

the_eleven

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Hi TJRAD, when I try to calibrate by moving the splined plastic cylinder (mine is black) and there is no effect. Hot water comes out of the spout at tank temperature.

Since my original post, I have flushed to cold and hot sides, and the thermal cartridge receiver part of the valve, and have also switched the check valves thinking that perhaps there was a problem with the cold side check valve. There was definitely ample flow from the cold side, so this confirms that there is no blockage in the cold lines.

The .pdf instructions you linked to your response mention a "green regulator nut" that is turned clockwise and counterclockwise. My valve does not have a green nut that can be adjusted with a screwdriver. Please see the attached photo.
 

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the_eleven

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Further adventures.... I figured out that the U-shaped stainless keeper clip that holds the black plastic ring which serves as the detent, need to be inserted for the inner temp regulating device to function properly.

Now I am getting a range of temperature, but only around 20° between full hot and full cold. According to Grohe, this valve should give a 40° range. Is there a way to adjust this as well?
 

the_eleven

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Apologies for all of the posts, but I finally determined the problem, which was detailed above and is due to my lack of understanding. When set to 100° at handle center detent position, the valve can provide the full 40° range. However, if set to 110° at handle center detent position, the valve only provides between 120° and 100°.

Thanks for all the suggestions!
 
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