Ignition failure on a gas A. O. Smith water heater usually comes from the igniter, gas supply, control valve, or a safety lockout, not a single simple fix.
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Quick answer
When a natural-gas A. O. Smith water heater will not ignite, the cause is typically a worn igniter or pilot assembly, insufficient gas supply, a faulty gas control valve, a tripped safety lockout, or a venting problem preventing the control system from allowing ignition. A homeowner can check basic supply and reset conditions safely; the igniter, gas valve, and venting components should be diagnosed by a licensed gas fitter.
Need a licensed gas fitter for your tank water heater? Call CANRO at (604) 359-1081 — residential natural-gas heating and hot water across Metro Vancouver since 1999.
A. O. Smith's residential gas tanks generally use one of two ignition styles: a standing pilot that stays lit continuously, or an intermittent/hot-surface ignition system that lights the pilot or main burner only on demand and monitors it electronically. The two systems fail differently. A standing pilot unit that will not light usually has an issue with the pilot assembly, thermocouple, or gas supply. An electronic ignition system that will not light more often points to the igniter itself, the flame sensor, the control board, or a safety lockout that needs a proper reset sequence rather than repeated cycling.
| Cause | Ignition Type Affected | Homeowner-Safe Check? |
|---|---|---|
| Closed or restricted gas valve | Both | Yes, confirm the shutoff valve is fully open |
| Weak or dirty igniter | Electronic ignition | No, requires inspection and likely replacement by a technician |
| Worn thermocouple or flame sensor | Both | No, licensed tech only |
| Failed gas control valve | Both | No, licensed tech only |
| Safety lockout after prior failed attempts | Electronic ignition | Follow the manual's reset steps once; do not repeat excessively |
| Blocked or disconnected venting | Both | No, requires inspection, do not attempt to clear vents yourself on gas appliances |
CANRO sees ignition failures more often in units installed in unheated garages, crawlspaces, or exterior-wall mechanical rooms, where cold-snap temperatures can occasionally affect ignition reliability, and in older homes where the gas line sizing or a shared meter serving multiple appliances leaves less pressure margin during peak demand. Damp coastal conditions can also corrode igniter electrodes and connections over time, particularly on units that are more than eight to ten years old, which is a common contributor to intermittent or eventual full ignition failure.
If your water heater sits in a laneway home or converted suite mechanical space with tight clearances, mention this to your technician, since combustion air availability is part of what gets checked when ignition is unreliable.
An igniter, flame sensor, or thermocouple replacement is a routine repair on a tank of reasonable age. A failed gas control valve on an older unit, especially one already showing tank corrosion or sediment issues, is a point where replacement often makes more financial sense than a major control repair. A. O. Smith's published service life figures are general guidance, not a guarantee, since real-world lifespan depends heavily on water quality, venting, and maintenance history.
Safety note
If you smell gas while attempting to light or reset the appliance, stop immediately, leave the home, and call FortisBC at 1-800-663-9911 from outside. Do not attempt to bypass a safety lockout or repeatedly force ignition attempts. Gas valve, igniter, and venting work must be performed by a Technical Safety BC licensed gas fitter. CANRO holds gas licence LGA0043870.
This is usually caused by a gas supply issue, a worn igniter or thermocouple, a failed gas control valve, or a safety lockout, and a licensed technician can identify which one applies to your unit.
Many electronic ignition systems will stop trying to ignite after several failed attempts as a safety measure. The manual usually describes a specific reset sequence; if that does not resolve it, the underlying cause needs to be diagnosed by a technician.
In some cases, a unit installed in an unheated or exterior space can have ignition reliability affected during a cold snap, though this is less common than a component fault.
If other gas appliances in the home are working normally, the issue is more likely isolated to the water heater's ignition components rather than the gas supply itself.
It is generally a routine, moderate-cost repair, but exact pricing depends on the model and is best quoted after an in-person diagnosis.
Follow the manual's instructions once; if it does not succeed, stop and call a licensed gas fitter rather than repeating attempts, since repeated ignition attempts on a real fault are not a safe long-term approach.
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