To further clarify,  the  cb for the 120Vac water heater element has no connection at all to the 12V circuit for the propane water heater system. You can be disconnected from 120Vac and/or have that cb off and it won't effect the water heater operation on propane. 

Except that if the 120Vac has already heated the water the propane heater won't need to run, or vice versa. 

Greetings:

If you look in the packet that came with the pod, you will find a book on the Suburban Water heater.  It has the wiring diagram for both the 120 and 12 volt systems.  The current flow for both go though the high limit shut off and the thermostats separate for each.  The 12 volt has a control module which contains the circuit for the ignitor and is wired back to the fault light, plus to the gas valve.  With a multimeter, you should be able to determine what part is at fault.  Be sure and shut off the 120 breaker at the panel in the camper before doing any trouble shooting.  I would think that most RV dealers would have the parts and there is always Amazon.

Crankster78  R-179  2015

 I have a mod you can search for if you want to add an adjustable tstat on the propane side to  bring the temperature down to something comfortable. Saves water while boondocking because you don't have to waste water while you're adjusting the temp. 

So, I suggest you try again to run the gas with the AC element on to be sure that what you think was happening was indeed the case. Shut both systems off and let everything cool off first or run some hot water out so that both systems will be calling for heat, then turn on the AC and then the propane. 

Originally posted by Jholler All good now. Seems the propane is locked out unless you throw the breaker for the electric water heater.

The LP and electric heating elements are totally separate.  If the LP is working since you flipped a breaker it's a coincidence.  Are you sure you have LP hot water and not electric hot water?

TT