[cgeis48]

After spending most of a day tracing wires, checking valves, calling Suburban and Keystone and pulling out my hair, I called the lead tech at the dealership; he explained that the gas-fired hot water system failed to ignite because the tank water reached a preset temperature that was too warm to trigger the LPG heater. Therefore, we had no hot water even though the electric water heater was turned on (I cant explain). It seems the electric water heater was only able to keep the water at a lukewarm temperature which is just enough to keep the gas portion of the heater from firing up. If you want a clearer explanation - call your expert.

He told me to open the outside water heater drain valve long enough to cool the lukewarm water in the tank. I did that, and after a minute the gas heater fired up; again we finally had hot water. After we showered we turned off the gas heater and (for unknown reasons to me) the electric heating element is working again. I know this is strange and not explainable - if you know why please share.
So, if neither LPG nor 120V heats your water, with both turned ON, try opening the drain or running a faucet for and extended time. The cold water could do the trick. It workd for me.