A flame dirty flame sensor can cause a furnace to light and go back off on a call for heat because the flame wasn't detected. Then it retrys until lock out. Not what the op described as happening. He said it randomly turns on for a minute and shuts off and other wise heats normally.A flame sensor with carbon on it sure can. The RHEEM and York units are notorious for that very symptom. Its the first thing I look at on a no heat service call for a 90's model RHEEM
There is no reason to pounce on my post. Your one of the few here I thought / think actually knows what they are talking about. That being said, I ( like you ) think the unit in question is much older then that tech. prolly so old that it has one heck of a crack in the exchanger and is pouring CO in the home. Who knows. The OP didnt provide much info and for all I know he knows just enough to get himself into a heap of trouble. Wasn't it just last month an entire family in Catoosa almost died from CO poisoning?
I meant that earlier post as good natured ribbing because I believe you are on the wrong track and made your comment about people not knowing what they are talking about. you seem like good guy and always try to help people here and that makes you ok in my book