This actually just started a day ago and I am trying to figure out as much as I can before calling a service person (if necessary). My apologies in advance if I am leaving out important details but I've never dealt with a faulty heater or A/C before.

My central heater in the attic was running for about 5 hours on Sunday morning according to the thermostat log but the house was quite cold that morning. When I tried to manually get it to turn on, I could hear it make a humming noise like it usually does when it starts and about a minute later the air started blowing. Unfortunately only cold air was coming out and after a few minutes the whole system turned itself off. So being curious I climbed up into the attic, read all the warnings on the outside of the unit, and proceeded to remove a few panels and look around. I did flick the on/off switch to the off mode for the outlet connected to the unit although I imagine the main breaker was the place I really should have turned off. I did not touch anything inside since all the "explosion" warning on the outside scared me half to death. I'm glad I read all the warnings about not potentially igniting gas with flames since I had gone up carrying a lighter thinking it was the good old fashioned piloted furnace (obviously not).

So now, after doing a few simple searches online, I am wondering if this is an ignition switch issue? Or a circuit board or fuse burned out? We were getting good heat until yesterday and now this happened. Now I'm losing sleep over how much this potentially might cost us.

One other note, when I opened the panel in front of the fan (between the intake vent and the part leading to the burning chamber) and found what looked like a loose sheet of filter material on top of the fan. From the adhesive backing, it looks like it was supposed to be attached to the ceiling part of the chamber but had fallen on top of the what appears to be the intake side of the fan. I removed it since it looked old and dirty anyhow.

I'd appreciate any advice or suggestions. I'll probably put out a service call this week but any insight would be great.