I had a similar experience a few years ago, not sure if this will apply to you or not. I was performing the annual maintenance on my AquaHot and for one reason or another, decided to start the generator (12500 QD in this case). It would run for a short period (1 - 2 minutes, perhaps) then stop. I restarted it and it repeated the same behavior. I may have done it once more before the real head scratching started. It then occurred to me that it was drawing air from the open end of the filter housing on the AquaHot (as I had the fuel filter off the unit as part of the annual maintenance). I replaced the filter and the "issue" was resolved.
