I was spinning it in reverse actually, but it would be enough to start the exhaust blower. It would also re-start pretty well for ~6 hours. It was probably the bearing. Also FWIW I have multiple carbon monoxide/air quality monitors and nothing tripped or alarmed.

Can you elaborate? I interpreted the same as the other comment that the blower fan just needed a hand start and kept going after the furnace started up. What you're saying only makes sense to me if the spinning the fan by hand allowed the furnace to start by bypassing the safety at startup, but wouldn't that mean that if the exhaust fan was stopped during normal operation (blockage etc) that the furnace would just keep going, dumping CO into the home?

From the description I thought that a degraded capacitor or lack of lubrication made the blower not start on its own, but the blower (and the whole furnace) would work if given a manual startup spin by hand.

The exhaust blower triggering a safety stop is normal when the blower should be blowing but isn’t. If the blower keeps spinning after it’s spun up manually everything is now working as intended. If it stopped blowing the furnace would go into safe mode again. Ask me how I know and I’ll tell you I had a broken blower on a cold winter before Gemini was a thing.

None of what you said is actually how furnaces work.

"Spinning it to bypass the safety" is not a thing.

Please don't spread FUD.

There are multiple continuous safety checks on such a system, and there was no risk of injury here. The fan itself is constantly monitored. Much more importantly, the pressure on the exhaust chamber is constantly measured (which can catch things like blocked outlets, a fan that might be spinning but not effective, etc).

If the exhaust fan couldn't maintain that negative pressure after the user stopped spinning it, the furnace would turn off again.

Their hack worked because the fan couldn't get the initial inertia up to speed (bad capacitor, dusty bearings, etc), but could maintain speed once it gets there. Have you never had an old home fan that would just hum when you turn it on but then work fine if you gave it the original crank? Same premise.

There was no risk here. If the fan didn't spin up to speed after that initial manipulation, and didn't constantly maintain the necessary flow, the furnace would have turned off again.

Welp, AI almost killing someone is definitely an "oh shit" moment.

https://www.covenantairesolutions.com/post/what-is-a-furnace...

“At its core, it's a small motor with a fan attached that has one primary job: to vent harmful exhaust gases out of your home before the burners ever kick on. This is the very first step in the heating sequence, and it's non-negotiable for a safe startup.“