Carlin burner keep tripping out

Hello all,



I have a Energy Kinetic EK1 oil heating system. The burner is a pretty much standard Becket/Carlin forced draft fan burner system. The Carlin 60200 primary control keep tripping out recently. I took the CAD cell connector, which resistance reads from infinite at idle to about 3K to 5K ohm when burner runs. The read is accurate cause I replaced the CAD cell with a new one, and it reads the same. So I guess this suggest the fire is not burning properly in the chamber.



My plumber had changed ignitor, nozzle, electrode, and ensured the oil supply/pump was running fine. But none of them changed the situation. I then tried a few things by myself. At one try, I accidentally left the ignitor cover unscrewed with 1/16 inch of opening, and the burner runs totally fine. I got CAD cell reading down to 100ohm in this case. Once I force close the cover, the CAD cell reading went back to 3K ohm.



Is there any suggest on what went wrong? Note that the chimney is only 3 feet high. Would it cause insufficient draft in the flue, thus cause fire problem in chamber. But how could leaving a 1/16 gap in ignitor cover solves the draft problem? Should I try cleaning the flue, or increase fan air inlet?



Any suggest is greatly appreciated.



Bill