Agilent 7820A GC: Back inlet shut down while front inlet bakeout

I'm trying to bake out the front column after inlet maintenance but the pressure of the back inlet cannot reach the set point and continues to shutdown, also resulting in a shutdown of the front inlet.  I've tried manually changing the back inlet pressure set point (i.e., set point was 23 but pressure wouldn't go above 22.3 psi; if I then change the set point to 20, the pressure cannot achieve that set point either).  Any suggestions?  My front column is a DB5-MS UI and the back column is DB-Select 624 UI, with attempting to bake out the front inlet at 250 degrees Celsius.

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