When the control board gets power (after fan runs, sails witch makes up, thru high limit switch) power is then applied to gas valve AND spark electrode.
Gas flows and is suppose to be ignited by spark electrode.....then when flame is established the spark electrode is used as flame proof.
If you smell gas......valve is opening BUT is not igniting either because of no spark OR electrode is not properly positioned
1/8" gap between electrode and ground rod plus electrode needs to be in flame path
You might also need to clean furnace/burner again......mud daubers/spiders/debris can really mess up the combustion air flow