I have a Trane XB80 Natural gas furnace and a Nest thermostat. It randomly decides not to turn on. When it's not turning on I go to the furnace and can hear a low humming which I think is either a relay inside on the circuit board or the small motor that turns on first to clear the fumes. If I cycle the power switch on the side of the furnace it will sometimes begin to work. Other times it will take more than one on/off of the switch. I changed the Nest thermostat (which has a common wire from a unit that converts from 4 wire to 5 wire) back to the old programmable thermostat that I know works and the furnace worked for a couple of days but this morning at 5 AM it went off again so that eliminates the thermostat. Unfortunately I didn't look to see what the LED was doing before switching the power but now it's working again. Next time I'll check that.
Has anyone seen this happen before and what was the fix?
Any help would be appreciated. I'm leaving for Florida in a couple of weeks and don't feel comfortable leaving with this going on. I live in Michigan and it's cold so pipes could freeze if it goes out when I'm not home.

 

First thing would be to get the error code the furnace is displaying. You should also check with your meter to verify an active heating call with your meter.
You should also see what exactly is humming. It’s not uncommon for transformers to make that kind of sound.