Furnace Heat Exchanger Borescope Inspection Ontario 2026: What It Is, When to Order One, and What the Camera Shows

What a Borescope Actually Is

A borescope is a handheld diagnostic tool with a small flexible probe, typically 5 to 9 mm in diameter, tipped with a high-resolution video camera and a ring of bright LEDs. The probe is usually one to two metres long so it can reach through an inspection port, the inducer housing, or the burner opening and snake around internal bends to view the inside of each primary heat exchanger tube. Modern units record video and still images; the better ones have articulating tips that steer around corners. Any TSSA-registered gas technician should own one or have ready access through their shop.[3]

Why a Cracked Heat Exchanger Is the Red-Tag Failure

The primary heat exchanger is the steel barrier between combustion gases and the household air stream. Fuel burns inside the tubes, combustion gas travels up through the vent, and the blower pushes household supply air across the outside of the tubes to collect heat. When that barrier cracks, flue gases can leak into the supply air stream. Carbon monoxide is the specific concern because it is odourless, colourless, and toxic at low concentrations, with Health Canada and CCOHS describing exposure as a cumulative health risk at chronic low levels.[4] Ontario residential code treats a confirmed crack as a red-tag condition: the gas supply is shut off and the unit is tagged until the heat exchanger or the furnace itself is replaced.[2]

How Common Is It?

Heat exchanger cracking is not common on young furnaces in clean operating condition. It becomes meaningfully common in the back half of a furnace's useful life. TSSA guidance points to 15-plus-year furnaces as the population where borescope-detectable degradation shows up at rates on the order of 7 to 10 percent, with most of those cases not visible to an external burner-compartment visual alone.[1] Cracks typically form at tube bends and weld seams where thermal cycling stress concentrates, and hairline cracks at these locations are often invisible when the furnace is cold and closed but open slightly as the steel expands during firing. A borescope pass performed with the burners running, or immediately after shutdown while the steel is still warm, gives a better read than a cold inspection.

When a Technician Should Order One

A borescope is not part of every service call. It is the appropriate next step when one of the following triggers is present:

• Rollout switch trip. The rollout switch trips when flame escapes the combustion chamber, which commonly happens when a blocked or cracked heat exchanger disrupts airflow.
• Flame rollout event. Visible flame escaping the burner box on startup is a direct combustion-chamber airflow problem. Borescope before restarting the furnace.
• Combustion analyzer reading climbing. A tune-up technician on a 10-plus-year furnace should read flue carbon monoxide. Numbers trending upward relative to the manufacturer spec, particularly above 100 ppm air-free, justify a borescope.
• Pre-purchase home inspection. Any furnace aged 10 years or more flagged during a real estate transaction deserves a borescope before the buyer takes possession.
• Unexplained CO detector trips. A household CO detector that alarms more than once with no obvious cause should trigger a borescope and a combustion analyzer pass on every gas appliance.
• Visible soot at the burners. Soot accumulation at the burner ports, particularly on a unit not previously dirty, is an early warning that combustion is disturbed.

On a clean, well-maintained furnace under eight years old with none of these triggers present, a borescope is not routinely required.[3]

What the Procedure Looks Like

A competent borescope pass looks roughly like this. The technician shuts off the gas, removes the burner assembly to expose the front face of the primary heat exchanger, and in some models removes small inspection covers on the back face. The probe is threaded into each tube in sequence. At each position the technician records video and watches for hairline cracks along weld seams and at tube bends, along with rust, scale, or soot.

On furnaces where the burner-side approach does not give a clear view, the probe is threaded through the inducer housing from the top, giving a view from the vent side into each tube. Some technicians use a smoke pencil as secondary confirmation: a cross-path smoke trace is a positive indication of a breach even when the crack itself is too fine to see clearly.[8]

A homeowner should expect either a written clean bill with representative still images, or a written diagnosis of any crack including which tube and the approximate location. A verbal “yeah, looks fine” is not an adequate borescope result.

What the Diagnostic Costs in Ontario in 2026

A borescope inspection is a diagnostic-only fee, not a repair. Typical Ontario 2026 pricing runs $150 to $400, added to a tune-up or service call. The low end reflects independent contractors bundling it with other work; the high end reflects franchises charging a premium diagnostic fee. The fee covers the technician's time, the tool, and the written report. If a crack is confirmed, the subsequent heat exchanger or furnace replacement is a separate quote. A heat exchanger replacement on a mid-tier residential furnace typically runs $1,200 to $3,500 in parts and labour in Ontario, often within a few thousand dollars of a full furnace replacement, which is part of why the decision tips toward replacement on older units.[6]

What Soot Inside the Tubes Means

Not every borescope finding is a crack. A common intermediate result is soot or dark scale on the interior tube walls. That is not benign: clean combustion leaves tube surfaces metallic and deposit-free, so soot indicates flame impingement, incomplete combustion, or airflow restriction, all of which stress the steel and accelerate fatigue cracking at welds and bends. A heavily sooted heat exchanger on a 12-plus-year furnace is a reasonable end-of-life flag even without a confirmed crack. A lightly sooted heat exchanger on a younger furnace is usually an airflow or combustion-tuning problem a good technician can correct.

Repair vs Replace Once a Crack Is Confirmed

The decision after a confirmed crack has two main inputs: the furnace's age relative to expected useful life, and the warranty status.[6]

A crack on a furnace under six years old is unusual and deserves a root-cause investigation (venting, combustion airflow, installation quality) before the repaired unit is returned to service. A failure that young often signals a persistent problem that will crack the replacement part too.

The Homeowner Pushback Playbook

The most common bad outcome is not a cracked furnace that goes undetected. It is a cracked furnace that a technician declared safe without actually looking inside. An external visual check does not see the inside of the heat exchanger tubes, and a single flue combustion analyzer reading does not prove the supply air is free of carbon monoxide.[5] When a technician hands over a safety declaration on a 10-plus-year furnace, a reasonable homeowner asks for one of the following before accepting it:

• A borescope inspection with recorded video of each primary heat exchanger tube, with a written report including model and serial numbers.
• A combustion analyzer reading taken in the supply air near a register with the furnace firing, showing zero CO in the supply, combined with a flue reading within manufacturer spec (typically under 100 ppm air-free for a conventional mid-efficiency furnace, lower for a condensing high-efficiency unit).

Neither requires exotic tools, and both are well within the routine capability of any TSSA-registered gas technician in Ontario. If the contractor refuses both, request a second opinion from a different company before the next heating season and document the original visit (invoice, technician name, what was and was not done) so the next contractor has context. Consumer Protection Ontario supports the homeowner's right to a written service record and to shop any major recommendation across multiple licensed providers.[7]

Where This Fits in Annual Furnace Maintenance

Most Ontario furnaces do not need a borescope on a routine tune-up. What they do need every year is a competent combustion-side check: a flue combustion analyzer reading, a visual of the burner flames, a review of the rollout and limit switches, and a scan of the inducer and venting. Those checks produce the warning signs that justify a borescope. Over a 15-to-20-year furnace life, expect one to two borescope inspections in the back third of service life, each triggered by a specific symptom. See the related guides below for adjacent symptoms tied to the same component.

Frequently Asked Questions

Related Guides

• Furnace Cracked Heat Exchanger Ontario 2026
• Furnace Roll-Out Switch Trip Ontario 2026
• CO Detector Placement Ontario 2026