November 18th

Now it's started getting colder, I've noticed that there's a problem with the eating - it'll run for about 10 minutes, then shut off.  The only way to get it to start again (that impatient me has found) is to go and flip the breaker - it'll start right up then.  So, while it wasn't too cold in the evening, I got up in the roof and checked the error code that the furnace is throwing:

Code 33: LIMIT OR FLAME ROLL-OUT SWITCH IS OPEN - If open longer than three minutes, code
changes to #13. Check for:
- Defective blower motor or start capacitor. - Dirty filter or restricted duct system.
- Loose blower wheel. - Defective switch or connections.
- Inadequate Combustion air supply Flame Roll-out Switch or fuse link.
- Open Flame Roll-out switch,or fuse link. Manual reset or replace.

Mean anything?  Nope, it didn't to me either.  So, I cleaned the flame sensor (even though it wasn't really dirty), then when I was testing it, I noticed that the filter was all bent out of shape.  That gets changed when the Nest controller says it's done enough hours, so I think it was a bad filter, and it's clogged up.  Changed that, and went on with the evening.