I am currently having a flow issue with my 6890N GC(w/ G1888 HS). I am doing yearly flow checks. Hooked up a calibrated flow meter to DET exhaust and turned off all gases (pressure off, makeup He off, Air off everything). I then enabled them one at a time at varied levels. FID= detector controlled gases worked fine and in spec. When I set the column flow the reading was low out of spec tried the varying levels still no go. Switched to the front which is a TCD. Same result detector controlled gases worked fine, but as soon as I went to do the flow through the column low. TCD was lower than the FID (TCD=1.36 on set of 2.5, FID was 1.8 on same setting). Checked gas filters they were old but no problem. 2 different columns but check all parameters and re installed to ensure good connection. Not really sure where else to go at this point. Any help or suggestion would be greatly appreciated.