This is the most serious type of red tag. Getting this type of red tag means the furnace or boiler in your home poses a serious danger to you, your family, your tenants, your guests and anyone else in your home or building. Generally, this means that a carbon monoxide leak has been detected and your natural gas provider is called to immediately turn off the gas.
This type of red tag is a warning tag. It means that you still have natural gas, but the clock is ticking. Repairs need to be made immediately to your furnace or boiler within the specified time period or the gas will be shut off indefinitely.