I have a ten year old Trane Forced Air Furnace in my attic that will not ignite. I have performed the suggested restart of the system with little success. The power is fine and the blower is working. The gas flow is fine, but it won't ignite. This problem started a couple of days ago, but I was able to restart the system. Had this same problem about a year ago and the service tech said the system just need to be cleaned. What can I do before have someone come out to just clean the system? Don't need I big holiday bill!
Does it have a hot surface ignitor or spark ignition? There should be a self test diagnostic on the unit. Also my guess is that if the gas flows but does not ignite it is probably a bad hot surface ignitor. It is mounted to the burner bracket, it has two wires connected to it and the wires have a plug socket, unplug it, remove the screw holding it and go get a replacement at graingers or Johnstone Supply. Your real problem is why did your HSI fail!!