Have HVAC Questions? Ask an HVAC Expert for Answers
Hi I'm Brian and I'm here to help! There are a few things that could cause this. If the furnace control board's fan circuit failed on, if the furnace had a high temperature limit switch go bad or a flame roll-out switch trip, it can cause this. If there is a short in the thermostat wire this can happen or even the thermostat could have failed to the fan on position. I would say the most likely cause would be a high temperature limit or rollout switch trip. Most times, rollout switches can be reset. They are located right near the burners and have two wires connecting them with a tiny reset switch between the two wire connections. Diagnosing this for certain may require some live voltage meter readings to be taken and I can certainly help with that if you are confident in your skills with a meter on live circuits.
Let me know if you have further questions on this subject. Otherwise, please remember to rate before leaving (3 stars or higher please!). Bonuses are always appreciated! Thanks for allowing me to help and thanks for using Just Answer!
Unfortunately I don't have, nor can I find, a manual or wiring diagram for your furnace. I have a pretty good idea of which model it is though. If you can take some pictures of the furnace including at least one with a close up legible copy of the wiring diagram, I can offer more help in trouble shooting.