Have you checked/cleaned all the condensate lines? Your furnace creates condensate (water) while operating. After many years of use, some of the drain lines can become plugged/restricted to the point it causes intermittent failure. It can be a pain and time consuming to clean all the lines and associated parts but sometimes it is all it takes to restore proper operation of the furnace.
A good suggestion. I've had water issues with my furnace in the past.....caused very erratic burner function. I GENTLY blew out the drain lines as well as the water separator and a couple sensors located inside that had hoses connected to them. I did that based on directions from my buddy who owns an HVAC company and installed my unit. This year I had him come and do a tune-up on my now 10 yr old unit....he tore most of the internals out....cleaned everything,blower,burners,water separator,hoses/lines,etc....surprising how much water and dirt can accumulate. We also installed a fancy wifi/Alexa T-stat...So far it's working perfect and the house is very comfortable. Your mileage may vary.
