I have a Heil gas furnace that just started acting up today the coldest day of the year here, go figure...

The pilot will light the burner and it will burn for a few seconds, but the main blower won't kick on. The burner then goes out. The draft fan runs fine. If I set the Thermostat to FAN instead of Auto, the main blower does function.

I think I have narrowed it down to the ignitor flame rod assembly. This furnace uses the Honeywell smart valve.

So does that sound like the likely source of my problem (ignitor)?

Thanks,
Chris

You might be correct. Clean the flame sensor carefully.

Sand paper works.

DO NOT clean the ignitor itself just the flame sensor part...

Well, replaced the ignitor/flame rod assy (after I fat-fingered it and broke the ignitor) and it did not fix the issue.
What it did turn out to be is there was a small amount of water (condensate?) inside the pressure sensing tube that was causing the snesor to think the chimney was blocked up and shutting down the flame. Blowing out the tube completely fixed the issue!

Thanks for the help,
Chris

Yep that can also be a cause as well as a few other items. I am glad you now have heat again.