We had the same deal on ours,Google Atwood mixing valve first,I pulled water heater removed valve,dissembled cleaned and reassembled. I also drilled the tamper proof glue from the handle so I can adjust the temperature to suit Me and re piped so I can adjust from an access hole now.
I'm sure the SAFTEY POLICE on here will scold me but be advised it's My Rv and Stewb asked for advise !!!! Not a horrible job except the white putty sealing the unit to the rv. Be sure to have some on hand before the task I did not !!!