Harry, I had a similar problem until replacing the control board on my furnace. It's my understanding that the need for frequent replacement can be a relatively common problem with hot surface ignitors, and it's often somewhat of a sign that the ignitor is either placed improperly in the flame path, or is not receiving the correct voltage. With yours sometimes remaining "on" it sounds like the reverse of my problem, which was the ignitor relay sticking "off," so you may be looking at a new control board.
Unfortunately, Harry, it sounds like time to break down and make the call to your HVAC repairman. Good Luck