Grohe mixing valve dilemna


Greetings All, I have a new 2nd floor shower using Grohe components. The first time using it, I realized there is no cold water flowing through the mixing valve. I can't modulate the water temp, only hot comes out. Providing there is cold water flow to the mixing valve, what could cause the water to not be coming out. The plumbers who did the install weren't too smart (I had to show them how to pipe the body sprays) and I'm wondering if they were too lazy to remove the insides of the valve prior to sweating the joints. If that's the case, can I replace the interior? Luckily I have a spare in case 2 valves were needed for sufficient water flow from all of the sprays, heads, etc..... Also, is it necessary to caulk the corners (floor and wall) in a tiled shower? I had a proper mud bed made, and he also used the brushed on red colored waterproofing coating. I realize that grout isn't truly watertight, so I wonder if caulk is necessary. Thanks to anyone who can help, Mark
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Single handle? Is it a case of the pipes being reversed? Will the cold come on when fully opened?

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With the water shut off at the main pull the valve and put a pail infront of the unit turn water on have you got water coming from both jets or ports where the valve goe's if so it is either the balancing spool or the valve . Did you remove valve when you soldered in the unit or did you put the valve in upside down possible ,have seen it done .
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Actually, I discovered an error while assembling the valve body handle. I now have cold water flowing. But still wondering about the caulk.....

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