Stormin Mormon wrote, on Mon, 22 Dec 2014 19:39:38 -0500:

Might have been someone, suggested low air flow, and a bad limit
switch. Trader, was that you?

Seems reasonable.

My hypothesis, at the moment, is that all the vents where shut
which (maybe) caused a "limit switch" to open up?

If only I could turn that limit switch back on.

I wish I could find a "master reset" which doesn't seem
to exist. I've pressed all the limit switch buttons I could
find already.

Here's the latest video after cleaning the flame sensor and
hooking up the DMM in DC amps mode at the 300ma range with
the flame sensor hooked in series with the DMM:
https://www.flickr.com/photos/98287134@N02/15464227533/

As before, the blower started up & then the induced draft motor
spun up, & then the igniter lit up orange, & then there were
flames which soon shut down. The flames happened three times,
all the while the LED blinked #34. When the flames died the
third time, the furnace shut down & the LED blinked #14.
https://c4.staticflickr.com/8/7521/1...32e0de5a_z.jpg

34 IGNITION PROVING FAILURE
- Control will try three more times before a lockout #14 occurs.
If flame signal lost after trial for ignition period, blower will
come on for 90 second recycle delay. Check for:
- Oxide buildup on flame sensor (clean with fine sandpaper).
- Proper flame sense microamps (.5 microamps D.C. minimum).
- Gas valve turned off. - Manual shut-off valve. - Low inlet gas pressure.
- Green wire MUST be connected to furnace sheet metal.
- Inadequate flame carryover or rough ignition.

14 IGNITION LOCKOUT
- Control will auto-reset after three hours.
Refer to #34.