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: 2026-08-07
What does a red tag on a boiler mean?
It means a certified gas technician found a condition that makes the boiler unsafe to operate, and documented it. A Type A tag means the gas was shut off at the appliance immediately. A Type B tag means the boiler can run until the date printed on the tag, after which the utility is notified and gas service to that appliance is suspended.
The distinction matters more with a boiler than with most appliances, because a hydronic system that sits cold in January can freeze and split pipe, radiators, or the boiler itself. If your tag is Type A in heating season, treat freeze protection as part of the job, not an afterthought.
Why do boilers get red tagged?
Boiler tags cluster around venting, combustion air, and the safety controls specific to a pressurized water system. The appliance itself is often fine; what fails is a control, a vent, or the room it sits in.
| Finding | Typically repairable? | What it involves |
|---|---|---|
| Blocked, corroded, or disconnected vent | Yes | Vent connector or liner replacement, then a draft and spillage re-test |
| Flue gas spillage into the mechanical room | Yes | Combustion air correction, liner resizing, or conversion to a sealed vent |
| Failed low-water cutoff | Yes | Control replacement and a proven trip test on start-up |
| Failed or missing pressure relief valve | Yes | Valve replacement, correct discharge piping to within 150 mm of the floor |
| Waterlogged or failed expansion tank | Yes | Tank replacement and system pressure reset |
| Gas leak at the valve train or piping | Yes | Repair, pressure test, and leak check of the affected section |
| Deteriorated masonry chimney serving the boiler | Yes, with another trade | Chimney relining by a specialist, then gas re-verification |
| Cracked or leaking heat exchanger / combustion chamber | No | Replacement of the boiler |
Which boiler red tags mean replacement?
A confirmed crack or leak in the heat exchanger or combustion chamber has no repair. Sectional cast iron boilers can sometimes be rebuilt if sections and gaskets are still available, but on most residential units the economics land on replacement. Everything else on the list above is a correction.
Age alone is not a defect. An old boiler that passes combustion, holds pressure, and vents correctly is a legal appliance. If a contractor cites age as the reason for the tag, ask which clause and which condition were actually found — that answer should be on the tag.
What happens to my heat and my pipes while the boiler is off?
A hydronic system with no heat source is a freeze risk once indoor temperatures drop toward freezing. Circulating pumps do not generate heat, and a system that freezes will split whatever gives first — usually a baseboard, a radiator valve, or an exterior-wall run.
Practical steps while you wait: keep the house above freezing with safe electric heat, leave interior doors open so heat reaches rooms with piping on exterior walls, and if the outage will run long in deep cold, ask about draining the system or adding glycol. Do not run unvented combustion heaters indoors.
How long does clearing a boiler red tag take?
Control and valve replacements are frequently same-visit or next-day work, provided the part is on the truck or at a local supplier. Vent and combustion air corrections are usually a day. Anything involving a chimney liner, an electrician for a power vent, or a full boiler replacement runs into a week or more, because it depends on another trade's schedule and on equipment availability.
Older commercial-style and discontinued residential boilers are the common source of delay. Control boards, gas valves, and aquastats for units past roughly twenty years can take days to source and are sometimes no longer made, which turns a repair decision into a replacement decision partway through the job.
How is a boiler red tag cleared?
A certified gas technician corrects the cited defect within their certification level, then verifies it. Verification is specific to the work: repaired piping is pressure-tested and leak-checked, venting work is confirmed with a spillage test and combustion readings under operating conditions, and safety-control replacements are proven through a full start-up and shutdown cycle including a trip of the control that was replaced.
Once it passes, the appliance is returned to service and the tag is cleared. Get written confirmation stating which tag it relates to, what defect was corrected, and what tests were performed, and keep it with the photo of the tag.
How we handle it
A TSSA-certified G1 technician reads your tag, tells you which finding you are actually looking at, and corrects what is in scope on site — piping, connectors, gas valves, safety controls, combustion air, and vent connections. Chimney relining, electrical, and masonry work go to vetted specialists and are sequenced so the gas verification happens last, not twice.
Send photos of your tag and we will tell you which category you are in. If your gas is already off, start with emergency red tag response.
Frequently asked questions
Can a red tagged boiler be repaired instead of replaced?
Usually, yes. Most boiler red tags cite venting, combustion air, gas piping, or a safety control such as the low-water cutoff or pressure relief valve, and all of those are corrected without replacing the boiler. A confirmed cracked or leaking heat exchanger is the main exception, because it has no repair.
Will my pipes freeze if my boiler is red tagged in winter?
They can, if the house drops toward freezing and the system holds water. Keep the house above freezing with safe electric heat, open interior doors so heat reaches piping on exterior walls, and ask your contractor about draining the system or adding glycol if the outage will run several days in deep cold.
Does a boiler red tag shut off my hot water too?
It depends on how your hot water is made. If domestic hot water comes from an indirect tank or a combi boiler, shutting off the boiler takes your hot water with it. A separate gas water heater is a separate appliance and is not covered by a tag issued on the boiler.
Can I use a different contractor than the one who tagged my boiler?
Yes. Any TSSA-registered contractor can do the correction, and choosing a different one does not invalidate the tag or restart the clock. The TSSA maintains a public directory of registered contractors, and you can ask any contractor for their registration and their technician's certification level.