When I researched tank-less water heaters for the house, I found out why they are so expensive, and why the don't work well on a RV.
There is a computer that monitors 3 parameters: the input water temperature, the input water pressure, and the rate/volume of the water flow. The systems on the RV's don't do this, and thus the problems. A sudden change in any or all of those parameters can result in getting scalded.
Home systems run on 120v only, at high amperage, and are far more sophisticated. The tech who explained it all to me said that the systems available for RV's just aren't quite ready for that application as yet.
2016 Redhawk 26XD
Me, Dear Wife,
2 Bluetick Hounds
1 Newfoundland / Black Lab Mix
1 Cairn Terrier