Welcome to the forum. Although you can post in any forum, the USA forum is here in case of local regs or laws
then get a local plumber to fit it
If you put location on here there might be someone who can do it for you
Had exactly the same problem, same mixer. Had to change the valve - about 70 quid. Took me some time to get it out of the body – got well stuck inside.
You will need some small allen keys.
Reply to the thread, titled "Shower problem." which is posted in Showers and Wetrooms Advice on Plumbers Forums.
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