New Kohler keeps maybe 1/2 the water in tank when flushing...is this by design?

Looking for some help with this mixing valve. Right now water is only luke warm. I got to the green dial and tried turning in both directions assuming this is how adjustment would be made. No change in temp. I looked at parts breakdown and wondering what the primary cause of this is. I am assuming the cartridge ? but curious what function the 2 valves play? Also assuming there are 2 service stops to shut off water? lastly any tricks on removing/replacing cartridge. Have done plenty of Delta/Moen and Symmons but this is uncharted territory lol Thanks [img]https://cimg5.ibsrv.net/gimg/www.doityourselft.com-vbulletin/640x480/img_3763_66b3f92f99adfa69c859fafff1adf3d2b3078298.jpg[/img] [img]https://cimg6.ibsrv.net/gimg/www.doityourselft.com-vbulletin/640x480/img_3765_85c8e4c7a54c5b04938e39397c2d6b46ec65938e.jpg[/img] nks

I am looking for a handled clamp or a wrench like tool to hold the shower valve (here, a Symmons single handle Temptrol) still while I unscrew the front cap (here a Symmons part T-12A)., to replace the cartridge. With the escutcheon plate removed, the entire valve body and about an inch of each of the 4 pipes (hot, cold, shower, spout) attached to the valve are exposed from the front. There is no structure behind the fiber glass shower stall within 8 inches of the shower knob on any side to have fastened the valve body to. Only the pipes hold the valve in position and just trying to unscrew the cap with just one wrench threatens to tie the pipework up in knots.