Water Heater goes on the fritz

I noticed when I was taking a shower that I had to turn the hot water almost on full which is not usually the case.  We checked later and found the water was hot but not as hot as usual.  After an internet search where we found people with the same problems but no solutions, Don called Atwood, the manufacturer.  They had him do a test on the heater which indicated it was the "mixer valve".  (Keep in mind a motorhome water heater is different from a house water heater.)  We decided we could live with the problem until we got some place where we could easily get parts - then the fault light in our control panel came on telling us there was another problem.  By this time of day it was too late to call Atwood again - more tomorrow.