When replacing the cartridge of a leaky Moen shower pressure balanced valve you may notice two white plastic rings behind the shower handle. Those two rings are actually a great safety feature called a scald guard.
The scald guard can help you restrict the temperature of the hot water to the shower. You can set the scald guard so that even when the water temperature is turned all the way to the hot side it will not get too hot. This is a great feature if you have small children that could get scalded by accident.
The adjustment to the temperature can be changed as needed so that when you no longer need the hot water restriction you can change it back.