Originally Posted by Frdbrkl
Have the nozzle and filter changed regularly (once a year should suffice) and clean the photocell.
Turn off the power to the furnace. On top of the burner assembly is a large black box-the transformer-which is hinged on one side. Loosen the screw(s) on the opposing side, and swing the transformer up and over. Follow the yellow wires from the reset control into the burner box and underneath the transfomer-torwards the back is the photocell or Cad Cell. It is usually held in place by a clip that just slides forward to remove it-clip, cell, and all.
Clean the cad cell with a clean dry cotton cloth, reinstall, making sure to tighten the screws securely-but don't strip them. Cycle the furnace. If you've changed the oil filter, nozzle, cleaned the cad cell, you may need a new cad cell. Repeat process, but this time pull Cad Cell out of holder/clip (it has 2 small round male pins on the end of it). Unfortunately I don't know where you could purchase one outside of Graingers.
