Warning tags are issued on any appliance or piping system that uses natural gas when a licensed gas technician has identified a hazardous issue. For example, if a defective heat exchanger is identified it can release carbon monoxide, an odourless and colourless gas, which can cause serious health problems if undetected. Carbon monoxide is harmful because it can rapidly accumulate in the blood, reducing the blood’s ability to carry oxygen.
If carbon monoxide is leaking from a cracked heat exchanger, there is a chance of it mixing with the air that is generated by the furnace and pushed through the vents. To prevent this danger, a red tag is applied to your furnace, your local utility is notified, and your natural gas is turned off.