I have a Heil furnace model number NUGK075AG02 (75,000 btu's) and the burner ignites for about 15 seconds then goes out and the fan continues to run. What might be the problem? Deka

Go to this post and clean the flame sensor. Post back with results. Do not touch the ignitor it is sensitive.

https://www.askmehelpdesk.com/heating-air-conditioning/armstrong-ultra-sx-80-furnace-wont-stay-287047.html

Thanks for getting back with me so quickly. Before I read your reply I found a loose pressure line hose which solved the problem. Thanks again and God bless! John 3;3 Deka

Yep a loose pressure hose will also do it. Glad you got it going.