no hot water electric or LP

Does the red light come on when you turn on the switch for using propane heating?

That whole side needs 12v to work the switch and the control board to operate on propane.

If the red light comes on you have 12v to the switch, but the switch might be bad. (or downstream the control board might be bad) Pull the switch out and get at the back of it to jumper the wires to see if now the burner lights. No joy, next get at the control board to see if it has any 12v.

Can't remember if the Suburbans need 12v to operate on 120v.

The unit only has 2 t-stats, one for each LP or electric. Not sure if this is right but the reset on either t-stat does not physically move or click when pushed.

Also the 120v breaker is ok.

Had a similar problem years ago on my previous camper. Turned out to be the thermostat (not the one on the wall of the camper, the one on the water heater itself). However, I did take mine into a shop and they fixed it. I would have never figured it out myself.

The gas does not try to ignite. Not sure this model has a mother board or is there a mention of a thermo sensor.

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.

There is likely a fuse in the fuse box.

honestly. sounds like the Mother board, or a bad thermo sensor

Does the gas flame ignite? If it does, check if the bypass valve is in the wrong position.