Is the Furnace Burner Flame Yellow and not Blue?
Natural gas is clean, safe and reliable. When your furnace is operating efficiently, natural gas burns with little residue release. However, if the appliance emits a flickering or a yellow flame instead of the normal blue, that is a sign that poisonous carbon monoxide is being created. Carbon monoxide is colourless, odourless, tasteless, highly toxic, and fatal.