I've got a similar unit it sounds like, Model Number 585EJ024050. I believe the pilot assembly part number is LH680005. At the beginning of winter the heater just plain wouldn't turn on. I crawled up on the roof and noticed the sparker was working but the pilot wouldn't light. I took the pilot assembly out, cleaned the orifice with a needle, put it back together and it worked. Since then it only seems to work intermittently. When I was on the roof I noticed the pilot stayed lit the entire time the burners were on - which I don't remember from last time I worked on it. Burners light but only for about five minutes. Odd thing is the blower kicks on, blows warm but not hot air for a little while, then stays on until the air gets cool. I didn't think these things had thermocouples, what the heck is causing the problem?