I have a Trane xl1200 dual fuel unit and am getting no heat. When switched to heat the exhasut fan runs for a bit and then shuts off, after awhile the fan forcing air into the house shuts down as well. During heat operation it goes from normal heat to aux heat display on the thermostat. I have tried going to emergency heat and the burners light for a short time, shut off, and then come on one more time before shutting down completely. I have tried shutting the gas off and back on as instructed but no help. I can not find a manual for troubleshooting so I am stuck. I did notice the unit could use a good cleaning, but am waiting for it to warm up to get the sprayer out. Any ideas or help would be appreciated.