Did they ask you to send it back?
May be a stuck fire switch or a short to the 510, but I think there is a problem with the board. Run over the contacts with a multimeter just to confirm the fire circuit is the culprit. You will have to touch top of flask to body to complete circuit to batteries (hence the sparking you saw earlier.
I unfortunately don't have a multimeter. I think they want it back don't know for sure. I also thought that the flask from Waidea didn't have a spring loaded 510, but this one has.
Also I'm scared to get another replacement of this as you never know it could start to auto fire at night and I wake up to a burned house
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