Our '13 23B had a gas only Atwood water heater. On the gas control there was a round blue disk that set the temperature. Our 5th has a gas/110v Atwood heater that is not adjustable. I've heard a lower temp thermostat can be used to change the temp. I've also read that, like Bed says, the bypass can be used to mix a little cold water into the hot-side outlet.
2013 F-350 CC SB 2WD 6.7PS
2013 Eagle Premier 351 RLTS
-SOLD- 2012 X23B
-SOLD- 2003 Ford Expedition 5.4, Bilstein shocks