Hi TONY. It was always after the water had already been hot for awhile. After I expereinced it a few times, I started asking around and doing a little research online and I found that other tankless heaters had the same problem. I don't know if all tankless heaters have that problem. I had the temp set at 130 degrees. it was a whole house unit (i.e. Point of Entry).
"Facts do not cease to exist because they are ignored." - Aldous Huxley (1894-1963)