If a licensed gas technician sees a furnace, boiler, fireplace, hot water tank or other gas appliance he deems unsafe or potentially unsafe he is required by the Technical Standards and Safety Authority (T.S.S.A.) to “red tag” the appliance.
The tag shown is provided by the T.S.S.A and is very common, but it does not have to be used. Any document which provides the same information is O.K.
The reason for the tag could be with the appliance itself, the venting (chimney), the gas piping or the electrical wiring. Anything that is deemed unsafe or dangerous or potentially so is a valid reason for the tag. Thus any part of the system which contravenes the gas code can be cause for a red tag.