Furnace carbon monoxide detector went off near heat in Greater Vancouver

If your carbon monoxide detector sounds when your furnace runs, treat it as the real thing first and the false alarm second. Carbon monoxide is colourless and odourless, so the alarm is the only warning you may get. Here is how Greater Vancouver homeowners should respond, and what could be behind it.

What to do the moment the alarm sounds

If the detector alarms and anyone feels dizzy, nauseated, has a headache, or is unusually drowsy, get everyone (and pets) out into fresh air immediately and call your gas utility's emergency line from outside the home. Do not go back in to investigate. Carbon monoxide symptoms are easy to dismiss as a cold or the flu, especially in damp Lower Mainland winters when windows stay shut for weeks.

If no one has symptoms, still move outside, open a door on your way out, and call the gas utility's emergency line before doing anything else. They can attend, check the air, and shut off gas if needed. A licensed technician should inspect the furnace before it is used again.

• Leave the home and get to fresh air right away
• Call your gas utility's emergency line from outside
• Do not re-enter to look for the source yourself
• Have a licensed technician inspect before relighting the furnace

Why a furnace can set off a CO detector

A gas furnace burns fuel to make heat, and a cracked or corroded heat exchanger, a blocked or disconnected flue, or incomplete combustion at the burners can let carbon monoxide reach the living space. Older furnaces in character homes around East Vancouver and New Westminster, and units tucked into tight basement-suite mechanical rooms, are more prone to venting problems because they share air with the rest of the house.

A detector placed within a few feet of the furnace or in the same closet can also nuisance-alarm on the small, normal spike of combustion gases right at start-up. That does not mean it is harmless, though. The only safe way to tell a venting fault from detector placement is a professional combustion and draft test.

• Cracked or corroded heat exchanger leaking combustion gases
• Blocked, sagging, or disconnected flue or vent connector
• Incomplete combustion or a dirty burner assembly
• Detector mounted too close to the appliance

When to call a licensed pro

Any CO alarm tied to the furnace warrants a licensed gas technician, not a DIY fix. There is no safe homeowner test for a heat exchanger crack or flue draft. After the utility clears the home, a technician from HeatLand can run a combustion analysis, inspect the heat exchanger and venting, and confirm whether the furnace is safe to operate.

Frequently Asked Questions

Could my CO detector just be old or faulty?

Detectors do expire, usually after seven to ten years, and a dying sensor can chirp or alarm falsely. But you should never assume that during an active alarm. Get to fresh air, call the gas utility, and have the furnace checked. Replace any detector past its printed expiry date.

Where should a CO detector be placed near a furnace?

Follow the manufacturer's instructions, but a good rule is to keep detectors out of the immediate furnace closet and instead protect sleeping areas and each level of the home. Mounting one right beside the burners can trigger nuisance alarms from normal start-up gases.

Is it safe to keep using the furnace after a single alarm?

No. Until a licensed technician confirms the heat exchanger and venting are sound, leave the furnace off. A CO source rarely fixes itself, and the risk of running it is too high.

Does a high-efficiency furnace still produce carbon monoxide?

Yes. Any gas-fired furnace produces combustion gases, including some carbon monoxide, which is why proper venting matters. High-efficiency models vent through sealed PVC, but a cracked exchanger or blocked vent can still create a hazard.

HeatLand Heating & Cooling is a licensed and insured, TSBC-certified HVAC company serving homeowners across Greater Vancouver. Our technicians diagnose the real fault, explain your options in plain language, and complete the work safely and to code.

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