I have a ~ 12 year old Carrier gas furnace. Most recently (at least it
occured at the end of the heating) it has failed. It will begin to
start, then ~40 seconds later automatically shut down. It does not
sound like there is ever any combustion (usually a noticeable sound).

Maybe 5 years ago, while I was on a trip, a similar situation
occured. Then my wife made a service call, where the repair guy
replaced the Ignitor.

Is there a way I can Now verify that the ignitor (~$22 part) has
again failed?

Might there be other likely causes, for our Failure to Start
situation?