… the burner simply stops heating, but since the thermostat is still in the on position, the fan that drives the (no-longer) heated air stays on. As a result, the furnace will pipe cold outside air directly into the house. One should think the furnace would be smarter than that.
Thus when I woke up this morning it was 40F inside. Nothing remarkable although it did feel colder than usual. I currently wear PJs and sleep under 6 layers of blankets some of which are folded double, so it is hard to notice until you get out of bed.
The fix is to first realize that you have run out in the middle of the night before the heater turns into an cooling unit. Second, to override the thermostat. This is easy if you understand how it works. Rather than messing with the coil, I just pointed an electric heater at it for 30 seconds.
After switching propane tanks I had it up and running again in 10 minutes. But it is a good thing to know in case you don’t have a backup tank.
In other news, I just updated my disclaimer. If there are any lawyers amongst the readers with an eye for these things, please have a look. I prefer not to go with the standard blurb, but obviously I also prefer it to be bulletproof against “I didn’t know hot coffee was hot”-lawsuits.