I have an attic mounted furnace unit, approx. 12 years old. Worked OK until last night. I can hear a "hum" like a small blower/fan coming on when I manually raise the temp. setting high enough, I can also see the "glow plug" cycling on and off for intervals of 30 seconds or so, for about 6 times, then it quits. While trying to start, I assume the next step would be for the main blower to "kick in" but it doesn't. I can't tell if gas (natural/Southern California Gas Co.) is flowing or not (but all my other gas appliances at home work just fine). Filter was dirty, but replaced now. Cleaned "glow plug" and surrounding areas from a little bit of dust and lint from attic. It works with a White-Rodgers 36E redundant gas valve hot surface ignition system. I tried turning it off, then on twice. No change. My abilities (or lack thereof) to further diagnose the problem forces me to stop right here and ask for help before I call a Tech and pull the credit card (not a good time right now) Any ideas/options? Thanks. Alex.

You need to take a closer look, when stat is calling for heat, the humming you spoke about,, check to see if the small (inducer) fan motor is running

The operation order should be

1st, the inducer fan comes on
2nd,the igniter comes on
3rd, the gas valve opens and the burners fire up
4th, the big blower comes on to blow hot air into you living area,

Check it out and let us know what isn`t working

Thank you for the info, I did not want to try anything else without some advice first. In order to check further, I had to remove the protecting lids (which in turn have a safety switch built in), I just didn't want to go blind. I'll check that and get back with more info.