Photo Cell Failure?

Have you tested the photo cell with a multi meter to make sure its really blown? one common problem with them is the eye gets dirty if the burner is not running clean. If the photo cell is burning out, then there is likely a problem with the control box and it is sending too much voltage or current though the cell.

Check the firing sequence, boiler backfires are known to damage sensors, and also frequent power failures can cause this.( during power failure the positive pressure is lost and some times the hot air rushes back towards the burner causing the photcell to overheat) Sensors are very sensitive to heat, i suggest using a tapping (plastic tubing from the blower/FD fan) and connect it to the photocell assembly. This stream of air will keep the sensor cool. Good luck, Chaterpilar