I would have called Gekko, told them to get their arse there and...

I would have called Gekko, told them to get their arse there and get it working to the specs that came with the plant. Otherwise I would tell them to watch social media as I expose their promised performance vs the actual performance of the plant.
And I would not accept the old red herrings about the rock types supplied initially. Its their plant, its their reputation, they've had bloody years to get it right and failed miserably. Otherwise replace it at their cost with one that performs in an acceptable manner. All imo of course.