You may find some wiring that looks like it has a fuse in the wiring right in front of the HWT. This is actually a fusible link that is designed to melt if for some reason there is a fire in the burner tube, usually from wasps building in it. This would then cut off the flow of propane by cutting power to the solenoid.
In my case I found the wiring to the fusible link had corroded and the link was no longer conducting through. After I cut off the wires and remade the connections to the fusible link, everything worked great again.
I got that information directly from calling Atwood service technicians on the phone.