Moen posit-temp single lever shower control When I turn the shower on, the water gets hot & stays (too) hot. I turn it almost off & feel a click, then slowly return to hotter temp & it adjusts fine. What do I need to do to fix this?

Sounds like you have something blocking the cold water side.

Turn off water, remove cartridge. Turn on water briefly to flush out valve. Reinstall cartridge.