Dometic comfort zone furnace turns off after 30 seconds

A bit more specific if it runs fore 30 seconds and shuts down (It should run for like 3 minutes) there is a LED on the control board (likely on the left outside) note if it is blinking 3 blinks pause 3 blinks repeated means "Ignition lockout"

Mine did that when the board failed to detect the burner was lit. oh the burner lit just fine but the detection chip was toast. New control board from dinosaur board fired 'er right up. No problem.

But you'd get the same indication if the burner did not light.