If you look at the Power switch located on the Hot Water Heater you will notice it has a small hole thru the rocker. This is for a small hairpin cotter pin that when stuck through the hole prevents the switch from being turned to the on position. When this is inserted it will avoid putting power to the heating element. Anytime the switch in the on position and the circuit breaker is also in the on position there must be water in the tank or the heating element will burn out. I make it a practice to avoid using the circuit breaker and always keep this switch in the off position until I hook up to water and shore power. I'm out of the coach anyway for the hookups and it only takes a second to flip that switch. I can only imagine the hassel to replace the heating element or the whole heater.
You can operate in both the A/C and gas mode at the same time, if fast hot water recovery is needed, we tend to use just propane when either boondooking or on the road and go to strictly A/C when using campground power.
The switch and red light indicator next to it in the power center is for propane operation.