Air intake restricted
Exhaust blocked
Edge connector on circuit board dirty
Main burner orifice clogged
Burner Head obstructed
Electrode faulty
Gas valve faulty
Circuit board faulty
Loose/corroded ground
These are issues that will prevent main flame from lighting off
Power to gas valve only happens for 6-8 seconds when spark electrode gets power
Check ground wire
Pull the edge connector....clean contacts on circuit board with pencil eraser and try again.
If that doesn't work.check voltage at gas valve during spark. No power/circuit board.
Got power....does gas flow. No/solenoid. Yes/clean burner assembly