LED ON and GAS LED Flashing
OR
LED ON light ON --- GAS LED light Flashing
Gas ignition FAILED
*Dirty/obstructed burner ...... debris fallen down blocking gas flow
*Spark electrode gap/position ..... 1/8" to 3/16" gap and electrode needs to be engulfed in main flame when it lights
*Spark electrode failed ..... check continuity/no continuity replace electrode
*Gas valve solenoid ...... is it opening when spark is occurring? Check solenoid resistance 80 ohms (gas valve only gets DC power for 6-8 seconds during sparking --- then power drops off if main flame doesn't light off)
*Check for DC Voltage on power module across terminals GV and GV GRD when trying to light off (No Voltage ,,,, replace board. Yes voltage ,,,,gas valve)
So basically........
Burner clean
Does it spark YES/NO
Does gas flow when sparking
Does it have DC Voltage