Hello folks, how do I troubleshoot an HVAC fan that doesn't stop? I wonder if it's the weather, it's so cold here down in Texas and maybe the cold is screwing up the components. There was a rotating power blackout these past few days, and when there's power we had to heat up. And a few hours later power goes out in the middle of heating operation.

I noticed today the fan keeps running (I think a bit low fan speed than when the thermostat is on heating). I have the Honeywell Whole House Ventilation. I just made sure all the wires in the HVAC is connected, but I noticed this service light lights up red sometimes (I hear the switch flick that I think it wants to turn off but it can't). It's a Honeywell W8150. Normal heating operation is okay, full blow speed and heat comes in, but when the thermostat comes off, the fan still runs. I checked the manual, but only when the service light is up alone, and the fan continuously runs on. This one has both, fan running and service light on (from time to time when the switch flicks).

I have a voltmeter to check just in case you want me to test something. Here is the manual.

Any input is appreciated. Thanks!