Have a 13 yr old Lenox furnace not staying lit continually. Lights for about 60 seconds kicks off for 2-3 minutes and back on again. Has a red light flashing. Anyone know what this could mean? Thanks

Click here (https://www.askmehelpdesk.com/heating-air-conditioning/heating-cooling-maintenance-repair-troubleshooting-frequently-asked-questions-58313.html#post268203) then go to gas forced air diagnostic codes. I'm guessing it is a weak flame signal sensed, go to what is a flame sensor, on the same page. Most Lennox flame sensor I have encountered are a bear to access, so good luck.