I have a Trane XL 6800 gas furnace and have replaced the ignitor and fan motor so far. My problem is everyother day or so the furnace shuts down and only the blower remains on and blows cold air into the house. I have an electronic honeywell thermostat. To fix the problem I have to shut the system down from the thermostat wait 20 minutes for the fan to turn off and then turn back on the furnace and it works for another few days. I did notice on my old thermostat that I only had a wire connected to the "R" and nothing attached to the "RC" so I wired the new theromstat the same way as well. I can't figure out why every day and a half the furnace does not light and I have to reset. Any suggestions would be greatly appreciated. Thanks!

Could be many reasons. Is there a diagnostic light somewhere on a board? It sounds like it is locking out because a problem keeps reacuring such as overheating main limit open. See FAQ on top of main HVAC page https://www.askmehelpdesk.com/heating-air-conditioning/heating-cooling-maintenance-repair-troubleshooting-frequently-asked-questions-58313.html
And https://www.askmehelpdesk.com/heating-air-conditioning/heating-cooling-maintenance-repair-troubleshooting-frequently-asked-questions-58313-2.html#post269282

I have a Trane XL 6800 gas furnace and have replaced the ignitor and fan motor so far. My problem is everyother day or so the furnace shuts down and only the blower remains on and blows cold air into the house. I have an electronic honeywell thermostat. To fix the problem I have to shut the system down from the thermostat wait 20 minutes for the fan to turn off and then turn back on the furnace and it works for another few days. I did notice on my old thermostat that I only had a wire connected to the "R" and nothing attached to the "RC" so I wired the new theromstat the same way as well. I can't figure out why every day and a half the furnace does not light and I have to reset. Any suggestions would be greatly appreciated. Thanks!!
Thanks for the help :) Do you think it could also be a faulty gas valve?

Thanks for the help :) Do you think it could also be a faulty gas valve??

Far less likely unless gas pressure falls too much after valve opens.

Thanks again I have a technican coming to check it today. I really appreciate your help :)