This happens to me often as well.  I have found that the mechanical pump can still pump fuel.  Try cranking the engine over a few times, then retry the boost pump.  Eventually it pulls the bubble through.  Once it starts,  watch your fuel pressure and perform a pretty healthy run-up to be sure it has cleared the system.  It only happens when parked hot for a fair amount of time, like while your eating lunch.. I always open my oil door to vent the hot air when parked.  This helps.  I have not found where this bubble forms, or how to stop it.  Tom McNerney
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