FAAS burner won't stay lit (240fs)

The struggles continue...

I've been having trouble with my 240fs, and I've arrived at a new problem state. The igniter lights just fine, and the burner head lights, but when I let go of the igniter button the igniter flame goes out immediately and then the burner head flame goes out after a few seconds. A few notes:

  • This is the air/acetylene burner head, I'm running the same "demo" method that we used for initial setup in 2020.
  • This is a fresh acetylene tank. In trying to figure out the problem, we swapped out the acetylene tank to make sure that wasn't the problem. I've adjusted the acetylene regulator pressure between 10 and 12 psi to see if that changed anything, it did not.
  • O-rings are all good. I was planning to change them in June as part of our annual maintenance, but visual inspection during cleaning looked fine (no obvious cracks, rings still pliable).
  • Spray chamber and burner head are clean. I've disassembled and cleaned everything a few times. I don't see any blockage in the gas paths and I can blow air through the spray chamber block when it's off the instrument.
  • The burner flame looks good (no gaps or sputters) for the ~second that it stays lit.

As the video shows, the igniter flame starts without any real problem/delay. The burner head takes a few seconds to light, that seems fine. The burner flame will stay lit as long as I'm holding the igniter button, but goes out when I release the igniter. When I release the igniter button and the burner head flame goes out, the instrument is detecting the "flame out" correctly and purges gas for a few seconds (as it is supposed to do). After the purge, I can reignite.

It seems like the acetylene flow to the burner head is coupled to the gas flow to the igniter flame. All of the external safety interlocks must be working because I can light the igniter and the burner head. I don't know if this is controlled more by the software or by an internal regulator/solenoid, but something is misbehaving that is deeper inside the instrument than I typically dig without some guidance.

Thanks for any help and have a great day!

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