Atwood water heater circuit board meltdown

A circuit has to "fault" low impedance for a fuse to open. If resistance remains high or open circuit the fuse for the circuit will continue to (be able to) pass current. I have seen various electronic boards catch fire because of unrelated outside ignition and burn the logic circuit to a pulp leaving the power side with fuse intact.

Any place that uses a controlled gas flame has a potential to become unstable. If flammable material sees the flame, then problems galore. Refrigerators and water heaters need to be inspected and serviced before they can damage themselves or thir surroundings.