A pilot light that keeps going out on a gas A. O. Smith tank usually points to a weak thermocouple, a draft, or a venting issue, not the pilot itself.
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Quick answer
A recurring pilot outage on a natural-gas A. O. Smith water heater is most often caused by a worn thermocouple or flame sensor, a draft disturbing the flame, dirt or debris in the pilot assembly, or a venting problem that trips a safety shutoff. A homeowner can safely check for obvious drafts and debris; anything involving the thermocouple, gas control valve, or flue should be diagnosed by a licensed gas fitter.
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On standing-pilot A. O. Smith tanks, the thermocouple or flame sensor is a small copper probe that sits in the pilot flame and tells the gas control valve it is safe to keep the gas supply open. As it ages, the probe's signal weakens, and the valve starts shutting the pilot off even though the flame looked fine moments earlier. This is by far the most common reason a pilot that used to hold steady starts going out repeatedly, and it is a straightforward, inexpensive part for a licensed technician to test and replace.
A second common cause is airflow. Water heaters in a garage, crawlspace, or utility closet with a door that gets left open to a draft can have the pilot flame disturbed enough to trip the flame sensor, even without a hardware fault. A third, less common cause is a partially blocked flue or intake, which can create backdrafting that snuffs the pilot; this is a venting issue, not a pilot issue, and needs a technician's attention because it also raises combustion-safety concerns.
Do not repeatedly hold the pilot button down and relight the flame more than a couple of times if it will not hold. Repeated relighting without addressing the underlying cause can mask a venting or gas control problem and is not a safe long-term habit. Cleaning inside the pilot assembly, adjusting the gas control valve, or working on the thermocouple wiring should be left to a Technical Safety BC licensed gas fitter, since these are gas-safety components.
| Step | Purpose |
|---|---|
| Measure millivolt output at the thermocouple | Confirms whether the sensing signal is strong enough to hold the valve open |
| Inspect the pilot orifice and tube for debris | Rules out a partially clogged pilot causing an unstable flame |
| Check draft at the draft hood or flue connector | Identifies backdrafting or venting restriction |
| Test the gas control valve's pilot circuit | Confirms whether the valve itself, rather than the sensor, is at fault |
| Review installation clearances and combustion air | Flags a room that is too tight or too drafty for the appliance |
CANRO sees this issue often in older Vancouver-special and character homes where the water heater sits in an unfinished basement or a converted laneway suite mechanical space with limited, sometimes changing ventilation. Coastal damp can also accelerate corrosion on flue connectors and draft hoods over the years, which slowly changes how a chimney or vent draws and can contribute to intermittent pilot problems that were not present when the unit was newly installed. If your tank is on an exterior wall or in an unheated space, cold-snap conditions can occasionally affect draft as well, which is worth mentioning to the technician.
If the thermocouple test comes back fine and the pilot still will not hold, the technician will usually move to checking the gas control valve itself, since valves can develop an internal fault that mimics a sensor problem.
A thermocouple or flame sensor replacement is a routine, low-cost repair regardless of tank age. If the gas control valve itself needs replacing on a tank that is already eight to ten years old or more, it is worth discussing replacement with your technician, since a new valve on an aging tank can be a significant repair relative to the value of installing a new unit. A. O. Smith publishes general service life expectations for its product lines, but actual lifespan depends on water quality, venting, and maintenance history, so treat any number as a general guide, not a guarantee.
Safety note
If the pilot outage is accompanied by a gas smell, soot near the draft hood, or a burning odour, leave the home and call FortisBC at 1-800-663-9911 from outside before doing anything else. Gas control valve, thermocouple, and venting work must be performed by a Technical Safety BC licensed gas fitter. CANRO holds gas licence LGA0043870.
This is the classic sign of a weakening thermocouple or flame sensor, which is a common, low-cost part to replace. A draft or venting issue can produce the same symptom, so a technician will check both.
A couple of relight attempts following the printed instructions on the tank is generally fine, but if it will not hold after that, stop and call a licensed gas fitter rather than repeating the process.
Yes. Airflow from an open window, a nearby exhaust fan, or a door left ajar can disturb the pilot flame enough to trip the flame-sensing safety, especially on older installations.
It is a routine, relatively inexpensive repair, but exact pricing depends on the model and site visit; CANRO can quote it after a short inspection.
If the gas control valve itself has failed on a tank that is already eight to ten years old, replacement is often more sensible than a costly valve repair on an aging unit.
Yes. A partially blocked flue can cause backdrafting that extinguishes the pilot and also raises combustion-safety concerns, so it is checked as part of any thorough diagnosis.
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