Okay some I'm a chick here and not too technically inclined but I had the same problem, found the sensor, couldn't get to it and couldn't figure out how to get screw out so I reached my arm into the hole with an emory board (for finger nail filing!) and I rubbed it around the sensor as best as I could for as long as I could stand to and voila!!
I have heat, it's running, the flame stays lit and my house has heated from 64 degrees to 67 degrees already and climbing! Thanks to all you do it yourself guys (AND GALS) for your help!! A repairman probably would have done the same thing in 5 minutes and charged me hundreds.