[Trainer]

Your Aqua Hot heater coolant overflow bottle is empty. Remove the radiator cap and fill lipping full with distilled water and engine antifreeze, 50/50 mix. When coolant tank is completely full and radiator cap back on, bring the coolant up to temp with diesel burner. When burner cycles off, use same solution to fill overflow tank to the hot line.

If you need gallons of antifreeze solution to fill the tank, no wonder you have hot water problems.

Congratulations on your mod. But my heater provides unlimited hot showers just fine in my 2001 motorhome.