Since I do not have a Surburan this is part conjecture but as I recall it's really two entierly seperate systems in one box.
The 120 volt system consists of the breaker back at your power distribution panel, wire to the water heater A pair of thermostats (primary and hi-temp) Switch and heat element. it has NOTHING to do with the Propane system
Which has a control board. two more T-Stats, and all the gas valves and ignition stuff.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times
