I am having exactly the same problem with my new to me 2000 16' Bambi. First owner, I assume in frustration, had the original water heater replaced in October last year wqith an Atwood model G6A-8E. And never actually used the trailer befor selling it to me.
I am sure the water tank is full & I have water pressure at sinks. I also can turn on the stove, cabin heater and refigerator so I am sure there s gas pressure. When I hit the switch I can here the igniter click but it doesn't fire up. Having someone else hit the switch while I stand outside holding a flame to igniter area the burner ignites twice, for a few seconds, with good flame then won't ignite again until red light switch is clicked again.
Previous owner is a neighbor of mine and is calling the installer to make an appointment.
I'm thinking some sensor is telling the heater that the heater tank is empty or water is already hot. Intend to buy a new dinosaur igniter board and try that.
Any other thoughts?