Guy takes shower, turns on hot, after 5 min the H20 Heater demands cold
water to fill the tank, this cold water depletes this guy's "cold"
water in the shower and thereby causes a surge in water temperature?"
Do you think that could happen or has that ever happend to anyone?


The water heater is demanding cold water to replenish what is going out the
shower head the second he turns on the hot, so this can't be it.

The only thing that would happen after 5 minutes is that the temp in the
tank drops below a threshold and the thermostat calls for heat (elements
turn on, gas burner lights, etc.) which would have no immediate effect on
the temp of the water.