Hello, my oil furnace is 18 years old. I have it serviced every year, last winter I had to reset it a few times so I called in a technician to diagnose why. They replaced the flame censor and made sure the airflow was good. He said it was in good shape and running efficiently. But I still needed to reset every couple of days. I had that company come back at least 5 times until they finally said, "sometimes you have to wait for it to completely fail for you to know what is really going wrong." So this fall I had it serviced by a different company and explained the problem. This company said it was an old relay and changed it. 5 days later I've reset it 4 times. Any idea what can cause this? I have honeywell control board and honeywell thermostats in my 2 zones.

So I have a weird problem with my goodman furnace. It's about 17 years old. The model is GMS81155CNA. I installed a nest thermostat last year when we moved in replacing an older non programmable thermostat. When I installed the Nest there was a blue wire in the wall that wasn't hooked up to anything. I used that as my C wire and hooked that up to the C terminal on the board in the furnace. Everything ran fine all summer and winter last year, as well as all summer again this year. In late october I had the furnace serviced as I did the year prior. The year prior I had a new blower motor installed. Everything checked out fine, the tech did his normal thing and we were good to go (tested before he left). Fast forward a few weeks and we had a string of colder weather...I noticed the furnace would go through it's normal process, but the flame would go out after about 5-7 seconds (sometimes longer, sometimes shorter). The fan would still kick on but would get cold air. Sometimes it would run for a bit, other times it would shut off after a few minutes. I believe the board was replaced at some point as there was paperwork near the furnace for it. I looked at the LED and saw it was flashing 8 times. I looked at the paperwork and it said that either the C terminal isn't grounded to the frame of furnace or I have a bad tstat. I'm trying to figure out what the actual issue is. It's very intermittent. I had the hvac tech come out and he cleaned the flame sensor... that helped for a week or two, then the problem came back. I changed the flame sensor out for a new one, but same issue still persists. I did notice there are two other wires in the c terminal besides the blue one that I used for t-stat. Last night I took those out and re put them back in and retightened it. It worked overnight and again this morning, but I'm just waiting for it to fail. I've attached some pictures of the board/wiring and the wiring diagram I have, I'd love to hear thoughts/suggestions. Do I really need to ground that C terminal somewhere else? If so why did it work all of last year and not this year. I did also recently replace the air filter so that is brand new. If there are any other/better pictures I can add let me know. [img]https://cimg5.ibsrv.net/gimg/www.doityourselft.com-vbulletin/920x2000/screenshot_20211227_073121_88f77600279d57e677c13aba233d11f81f662ffa.png[/img] [img]https://cimg7.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x1504/pxl_20211227_121501180_8821efefa5af2f04cc5dd4c579308706759c6170.jpg[/img] [img]https://cimg0.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x1504/pxl_20211227_121528118_bc8991297c9f8fa54b364206f550481e5d7b088e.jpg[/img] [img]https://cimg1.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x1504/pxl_20211227_121534499_aeadb9c5612ab0cff3d327c920cdbec30634f27c.jpg[/img] [img]https://cimg2.ibsrv.net/gimg/www.doityourselft.com-vbulletin/1500x2000/pxl_20211227_122418119_3af270bdf2003042e430c5b2ecfb327e9f248c0e.jpg[/img] [img]https://cimg3.ibsrv.net/gimg/www.doityourselft.com-vbulletin/1500x2000/pxl_20211227_122434445_91c11076c30ba461818d42144e3e8775353e16d8.jpg[/img]