[sourdough]

First; is there water in the hwh? Check as pointed out above.

If it is full, then proceed.

Will it work on propane? It should irregardless of the AC portion or not. To check some of those things you will need to know if its Atwood or Suburban - differences in the way they operate.

Won't work on anything? Check voltages at the control board. Mine is an Atwood and had blown a tiny little fuse on the control board; unfortunately the fuse blew due to a defective diode. Cure? Replaced the board.