Quick answer
A red tag on your furnace means a certified gas technician found an unsafe condition and was required by Ontario's gaseous fuels regulation to tag it and notify the gas distributor. A Type A tag is an immediate hazard: the gas to the appliance is shut off on the spot. A Type B tag lets the furnace run until the deadline written on the tag.
A red tag on your furnace in Ontario means the appliance failed a safety check under O. Reg. 212/01, the gaseous fuels regulation enforced by the TSSA. The technician who finds the condition has no discretion: the rule requires a warning tag on the appliance, a written notice to you, and a copy sent to the gas distributor, which across Halton, Hamilton, Peel and Toronto is Enbridge Gas. Whether you can keep using the furnace depends on one letter on the tag.
Type A versus Type B: can I still use the furnace?
- Type A: the condition is an immediate hazard. The technician shuts off the gas to the furnace, or at the meter if the appliance cannot be isolated, and the furnace must not be used until the problem is corrected.
- Type B: the condition is unacceptable but not an immediate hazard. The furnace can keep running, and the correction has to be completed by the expiry date written on the tag.
Read the date on a B tag, not a number from the internet. Enbridge's published guidance gives up to 42 days for repair or replacement, and the technician writes the actual expiry on your tag. If Enbridge has not received proof of correction by then, it is required to shut off the gas to the appliance, and to the whole house if it cannot get in to reach the furnace.
Using a tagged appliance past the expiry, removing the tag or reopening a valve closed under an A tag is illegal, and it leaves you running the exact fault someone measured. A January B tag is a deadline to act on in the first week, not the last.
The usual reasons a furnace gets red-tagged
- Cracked heat exchanger. Flue gas can mix with the air going to your registers. Usually an A tag; see whether a cracked heat exchanger is an emergency.
- Venting defects: a separated plastic vent joint, the wrong pipe material, a corroded chimney liner, a vent terminating too close to a window.
- High carbon monoxide in the flue gas on a combustion test, from dirty burners or the wrong gas pressure.
- Missing clearances to combustibles: storage, framing or finished walls built too close to the cabinet or vent, common after a basement renovation.
- No combustion air, a gas leak at the furnace, or a safety switch that has been bypassed.
The tag itself lists the condition and a code reference. Ask the technician to show you the reading or the defect while they are still in the house: a combustion printout, a photo through the inspection camera, the gap at the vent joint. A legitimate tag comes with evidence.
How a red tag gets cleared
- A certified gas technician corrects the condition: repairs the venting, replaces the part, or replaces the furnace.
- That technician confirms the appliance is code-compliant and completes the clearance section of the tag with a name, certificate number and signature.
- The clearance goes to Enbridge. On a B tag, have it sent well before the expiry date so it is processed in time.
- Only then is the appliance put back into service by the technician. If Enbridge shut the meter off, Enbridge restores it.
Any TSSA-registered contractor can do the correction; you are not tied to the company or the utility that wrote the tag. If the diagnosis is a cracked heat exchanger and the next sentence was a sales quote, a second opinion on a red-tagged furnace is reasonable, though it does not extend the deadline.
Repair or replace a red-tagged furnace: what it costs
The cost depends on which defect is written on the tag. Venting and clearance problems are often repairs; a failed heat exchanger on an older furnace is usually a replacement.
- Diagnostic or second-opinion visit: $90–$150.
- Most furnace repairs, including burner cleaning and safety switches: $150–$800.
- Draft inducer motor: $400–$900.
- Replacing the heat exchanger: $1,500–$3,000 for parts and labour.
- New high-efficiency furnace installed: $4,500–$7,500.
The rule we use at the kitchen table: if the repair is more than half the price of a new furnace and the furnace is past 15 years, replace it. A heat exchanger still under the manufacturer's warranty changes that math, so have the model and serial number checked before you decide.
ZK Mechanical clears red tags across Burlington, Oakville, Milton, Hamilton and Mississauga: a TSSA-licensed technician corrects the fault, files the clearance with Enbridge and relights the furnace. Start with furnace repair or the dedicated red tag repair service, call (647) 801-1252, or tell us what the tag says through the contact page. Related safety questions are grouped in the emergency answers hub.