A defective Spark Electrode will have microscopic cracks in the white Porcelain insulator. These cracks will allow the Hi voltage current to spark to the burner. BUT, these cracks will "leak" the return ac signal that signals the flame. This means the board does not see the return signal that shows the flame. Hence it goes out. I have NEVER replaced a gas valve for intermittent operation. They either work or they don't. I cannot remember replacing a gas valve in the past 10 to 15 years, other than one leaking. I have worked on thousands of refers over the years. Doug