It could be a valve allowing hot and cold water mix Moen fixtures are notorious for this maybe the tub/shower valve or faucet go to the water heater and shut off the hot water and go to some faucets/fixtures turn on hot see if it ever shuts off if it doesn't you know its mixing somewhere if it does go flush the toilet a couple times see if it shuts off there too that will tell you if it's hot water or water mixing.

Benjamin Franklin Plumbing
153 Garden Park
Orem, Utah
(801) 960-1565