The solenoid may be stuck. Or debris prevents it from closing. Try unplugging and replugging it. And if you are willing to open it. Clean it with alcohol. Don't add oil or liquid lubricant (such as silicone) because it will block the movement of gas from one side to another side of the plunger, making it more prone to get stuck. If I need to lubricate it, I would use a teflon spray lubricant.