Spark electrode gap to ground is 1/8"
Gas valve is only open for 6 seconds or so WHILE voltage is sent to spark electrode.
IF main flame does not light off and PROVE voltage is dropped from gas valve and another ignition sequence is attempted.
IF Spark Electrode gap is too wide/narrow.....tough to generate enough 'heat' to light propane
IF Spark Electrode is not directly in path of propane.......harder to get it to light
IF Spark Electrode ceramic is cracked......voltage can jump to ground in wrong area
Have you WATCHED it while attempting to light?
Good Strong Spark?
No false tracking.....jumping to ground?
DO you hear gas solenoids click when energized?
Does main flame light then go off? Or not light at all until several attemts?