Completed annual maintenance on one gas furnace, changed return filter 16x25x1, cleaned flame sensor, cleaned burners and inside burner box, inspected heat exchanger which no signs of cracks, tested capacitor which tested in range, tried to fire furnace and gas valve opened but igniter didn’t glow, pulled igniter and found very worn and a crack in middle rod, replaced with new igniter and system fired right up, took combustion test which everything looked normal, 70 degree difference in temperature, system operational and working,