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?

  • What is the make and model of the furnace? Are there any lights, or other indicators that would display what caused the furnace to stop? You said that the thermostat fan switch is set to ON or FAN, is this correct?
    – Tester101
    Feb 6, 2015 at 14:16
  • @Tester101 - It is a Payne PG8MAA payne.com/pg8maa.html - Yes the fan switch is set to ON so that it runs 24/7 (or is supposed to). No indicators that I can see.
    – Nelluk
    Feb 6, 2015 at 14:37
  • When the thermostat calls for heat, does the hot surface ignitor turn red? Does the gas valve open (should hear a click, clank, or bang)? Can you hear, or smell gas?
    – Tester101
    Feb 6, 2015 at 16:22
  • @Tester101 - If this helps, when I woke up to find the system silent I did open the utility closet and I could feel heat coming off of the otherwise-quiet furnace and could smell gas (or at least, it smelled like an operating furnace).
    – Nelluk
    Feb 6, 2015 at 21:51
  • You should contact a local HVAC company, as it sounds like you may not have much experience with HVAC systems. It could be a million different things, but without observing the furnace it's nearly impossible to narrow that down.
    – Tester101
    Feb 6, 2015 at 22:05


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