We have 2018 23CB. Our hot water heater heats with both Gas AND Electric at the same time when we turn on just the electric switch. Turning on the gas switch heats with propane only.
This is our second Airstream. Our previous 2013 model heated with electric only with the electric switch on. So having gas and electric together does not seem right.
I did check the hot water heater wiring diagram. Switched 12V
is used to control gas and electric operation. I verified the gas and electric switches are wired correctly. However turning on only the electric switch places 12V
input to control board for both gas and electric (white and orange wire). So it appears to be wired to operate this way.
If the electric switch is not supposed to turn on gas and electric together, I'll need to further chase the wiring to find out where the problem is.