chasfm11 wrote:

OK.

First, there are a couple of different brands of water heater that are used on all types of RVs. Open the outside cover and see if you can find and model.

Things you can check.

1. Turn on all of the burners of your stove at once and make sure that they all burn with a blue flame. Because you have propane in the tanks does not insure flow to the water heater. The stove test won't either but it gives you some feeling that there is adequate flow.
2. Verify that you have a solid 12volts on your batteries. The control board won't work well if the voltage is too low.
3. If it is an Atwood, you should be able to see the control board when you take the outside cover off. Mine is on the righte. There should be a high voltage lead in the center of the board that goes to the igniter. Carefully take that wire off the board and clean the contact with a pencil eraser. Atwoods do "flame sense"(the board checks that there is ignition or it turns off the gas after a few seconds) through the igniter. You have the "no flame sense" symptom.
4. As others have suggested, you could have a blockage. Mud daubber wasps can build nests in the combustion chamber and spiders can build webs over the gas valve nozzle. On my Atwood, I can easily see the combustion chamber and the tube from the gas valve is easy to remove.

I had similar symptoms to your water heater on my Atwood water heater. It turned out to be the board. Those are not cheap ($100-150) so replacing the board would be my last resort.