Quote Originally Posted by bryjcom View Post
They usually just check for CO and then red tag it or shut it down and tell you to call an HVAC company.

They don't determine what's causing it, just whether its coming from the vents, or flue pipe, or furnace burner compartment, etc, etc.
This was where I was headed. Tough time to get shut down then have scramble to get repaired during busy season and sub zero temps.