The blower on my furnace is set to be on constantly. The last two nights in a row I have woken up in the middle of the night to hear that the blower is not running and that the temperature is dropping quickly.
Both nights I got up and turned the system off entirely.
Morning 1: Turned system back on, and it seemed to just blow cool air after running for five minutes. So I opened the furnace and pulled the filter, and found that someone (oops) had installed it backwards. Put it back in the right way and turned the system on, and it started blowing hot air. Eureka! I've solved it.
Night 2 the same thing happens, so I turn the system off and go back to sleep.
Morning 2, this time when I turn it back on, it works normally and is blowing hot air.
Any suggestions as to what this could be?