By now I know the drill: the boiler isn't firing. Time to head downstairs and work my magic, since I've done it so many times before. It's actually been working well since I replaced the ignition wire, and this is the first time it's acted up since.
I take off the access panel and look.
No pilot light. I can hear it trying to spark.
This is a bad thing. Where before the pilot light was on fine but the flame sensor wasn't working, this was simply no flame at all. It could mean a problem with the gas line, or the gas valve on the boiler itself, or that I've been disconnected...
Sinking feeling. Though it seems odd that I'd get disconnected on a Friday night. Maybe they did it in the afternoon and it's just taken this long for the house to cool down...
Okay, let's not panic just yet. I had a grill lighter downstairs, let's see if I can light the pilot manually.
(click, click, FOOM!)
And it works. It's not a gas problem after all, it's an ignition problem. And the only thing different is the ignition wire that I had replaced, so the first place to look is obvious.
I disconnect the flame rollout sensor to shut off the ignition system and take out the burners to look at the wire: The insulation had burned through enough that the spark was grounding out before the igniter.
I grab the old ignition wire that I had saved and cleaned up and replaced it; it took maybe 15 minutes from start to finish. Clipped the leads back on and she starts up like a champ again.
The heat is back on. It's warming up slowly again-- another hour and it will be back to normal. In the meantime, I need to cobble together another replacement ignition wire from some high-temperature silicone-insulated wire, if I can find any. If not, I'll have to find some high-temp silicone tubing of the right diameter and make something.
Slowly but Shirley, I'm getting this thing fixed.