Can Hot Water heater be set to Propane only?

Quick question this weekend i noticed when plugging in my generator that it was drawing more power than i expected, this is because the hot water heater kicked on because i was plugged in.

The generator immediately revved down once i dropped the outside panel flipped the switch on the hot water heater to OFF.

I tried igniting the hot water heater with that switch in the OFF position and it didn't seem to work. Should I be able to run on propane with the outisde hot water heater switch in the OFF position?