What is the supply pressure for your air at the back of the GC? It should be set at a min of 55psi to a max of 100psi. I usually like setting my tanks at 80 psi. If the pressure is ok, then you could have a jet that is restricted and needs to be replaced.
You can try to reinstall the column. Be sure you fallow the instuctions for your Inlet. Use new ferrules.
After you disconnected your Column check if the path from the inlet is free. ( use a very this needle. We used an old CG needle for that.
And when you do this, just change the Jet as well.
Reinstall the column and tighten it with your hands. When u did it use the tool and only go for another quarter round.
Not to tight, or you might destroy the ferrule.
Close the oven and try "safe" settings. put the makeup gas the last.
Also check if the gas flow to the device around 6 bar or 90 psi is.
I hope I helped you.