Anthony — TSSA-Certified G1 Gas Technician
TSSA G1 licence #TBD · 15+ years in gas and mechanical trades · Service area: Greater Toronto Area, Ontario
Last updated: 2026-08-03
What actually gets a furnace red tagged?
The most common triggers are a cracked or corroded heat exchanger, flue gas spillage into the house, a disconnected or blocked vent, and improper gas line connections. Any one of these can put carbon monoxide into living space or create a fire risk, which is why the technician doesn't have discretion to leave it running.
Furnaces installed without permits, or modified by unlicensed people, are also flagged. Age alone doesn't cause a red tag — a 25-year-old furnace that vents and burns correctly can pass, while a 3-year-old unit with a cracked exchanger cannot.
| Condition found | Why it's dangerous | Typical fix |
|---|---|---|
| Cracked heat exchanger | CO can leak into supply air | Replace furnace |
| Flue gas spillage | CO/combustion gases enter house | Fix venting, re-test draft |
| Blocked or disconnected vent | Gases have nowhere to go | Clear or reconnect venting |
| Unlicensed gas line work | Leak or improper pressure risk | Re-pipe to code, pressure test |
| Missing or failed permit | Unverified installation | Retroactive inspection/permit |
What does the red tag itself mean?
A red tag is a physical notice attached to the appliance and its shutoff valve stating the gas supply has been disconnected because the appliance was found unsafe to operate. It is not a suggestion — reconnecting the gas yourself or removing the tag without proper inspection is a violation of Ontario Regulation 212/01 and can void your home insurance.
The tag stays in place until a TSSA-certified gas technician inspects the corrected condition and signs off. In the Greater Toronto Area, this applies whether the finding came from Enbridge Gas, a home inspector, or an independent technician.
Can a red-tagged furnace be repaired instead of replaced?
Sometimes. Venting problems, blocked flues, and loose gas connections are often repairable within a day. A cracked heat exchanger is not repairable — it requires furnace replacement, because the exchanger is a sealed pressure-formed part.
An inspection will tell you which category you're in before you spend money on a guess.
- Technician re-inspects the exact condition noted on the tag
- Determine if it's a repair (venting, connections) or replacement (heat exchanger)
- Complete the fix or install the new furnace
- Combustion and draft testing to confirm safe operation
- Gas technician signs off and removes the red tag
How long does it take to clear a furnace red tag?
Straightforward venting or connection repairs are usually resolved same-day or next-day once a technician is on site. A full furnace replacement typically takes 1-3 days from quote to install, depending on equipment availability and whether ductwork changes are needed.
Winter months in the Greater Toronto Area can extend wait times for furnace replacement due to demand, so getting the diagnosis done quickly matters.
What does it cost to fix a red-tagged furnace?
Venting or connection repairs generally run $150-$600 CAD. A full furnace replacement in the Greater Toronto Area typically runs $3,500-$7,500 CAD depending on furnace size, efficiency rating, and any duct or venting work required.
Get a written diagnosis before agreeing to full replacement — a legitimate technician will show you exactly what failed and why it can't be repaired.
Do I need a permit to fix a red-tagged furnace?
Furnace replacement requires a mechanical permit in most Greater Toronto Area municipalities, and the installing technician typically pulls it. Repairs to existing venting or gas lines may or may not need a separate permit depending on scope — your technician can confirm before starting work.
Any electrical work tied to a furnace swap, such as a new dedicated circuit, is coordinated through a licensed electrical partner contractor, not performed in-house.
Frequently asked questions
Can I just relight the pilot or reset the furnace myself after a red tag?
No. Tampering with a red tag or reconnecting gas without a certified technician's sign-off is a violation of Ontario Regulation 212/01 and can leave you liable if something goes wrong. The tag has to be removed by a TSSA-certified gas technician after inspection.
Will my furnace red tag show up if I try to sell my house?
Yes. Home inspectors routinely check for red tags, and an unresolved tag will surface during a buyer's inspection or when the buyer's insurer asks about the mechanical systems. Clearing it before listing avoids delays at closing.
Does a red tag mean my furnace is unsafe forever?
No. A red tag reflects the condition found at the time of inspection. Many tags are cleared with a repair to venting or gas connections; only conditions like a cracked heat exchanger require replacing the furnace.
Who is allowed to remove a furnace red tag in Ontario?
Only a TSSA-certified gas technician can inspect the corrected condition and remove a red tag. This applies regardless of who issued the tag originally, including Enbridge Gas or a home inspector.