Easiest thing first:
Do you have propane in your tank(s) and are they open so propane can get to the water heater. The heater will try a few times to ignite then go into lockout mode if it fails to light. You have to turn off the inside switch, then back on to reset the lockout.
Does your furnace work, and/or stove currently....to see if there is a propane delivery problem.
2011 Flagstaff 831 RLBSS
I used to be addicted to time travel, but that's all in the past now.