SG1 will be a spark generator
It sends a high voltage pulse to jump an air gap - the spark lighting the pilot flame - if the high voltage finds an easier route it will run to earth the easy way and the pilot flame will not light.
Make your test with the lights out or with a coat over your head - see exactly where the spark is going - try to make it work correctly - it may be that the spark is being attracted by some conductive dirt.
Otherwise replace the circuit board yourself or have a professional do it.
Good luck...
PL Travers (Mrs)
September 2014