Agilent G7111A pressure problem when using helium blanketing

Hello. Agilent 1260 with G7111A pump user here.

When using a mobile phase reservoir blanketed with helium (6 PSI overpressure on mobile phase bottle), the pump won't pump solvent. Just stays at 0 bar. If I remove the helium pressure, the pump immediately works as normal. 

I've used this exact setup on an old system without issue, so I don't understand why this is happening. Anyone got an idea? 

Thanks in advance for any help! 

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