As suggested ^^^^
Soot/carbon build up on spark electrode will impede the 'Flame Proving' circuit as will a dirty/loose spark electrode wire connection
Electrode has to be 'engulfed' in Flame when it lights
Is it time for YOUR Medication or Mine?
Dodge 3500 w/Tractor Motor & NUWA 5vr
US NAVY---USS Decatur DDG-31