Flame has to PROVE it lit or circuit board shuts down DC to gas valve.....don;t want raw fuel flowing (BOOM)
Spark electrode is used as return path for flame lit signal (miliamp signal generated by the flame--rectification---ions etc)
Anyway.this miliamp signal goes back to circuit board proving main flame is lit so circuit board holds DC on gas valve until thermostat reaches set temp point...then DC is stopped by t-stat
Mis-aligned electrode, dirty electrode (soot/carbon), dirty/loose high tension for spark electrode, cracked ceramic insulator, poor ground
Above are 'common' issues...could be more involved (gas leaks, obstructed exhaust, circuit board issues, low LP pressure ----furnace is biggest hog of all appliances)
Under warranty......let them pull it apart and fix
