Ignition failure is one of the most common reasons a boiler stops producing heat, and it is also one of the more methodical faults to diagnose once you know the sequence involved.
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Quick answer
Ignition failure on a Noritz boiler is most commonly caused by a fouled or worn igniter, a flame sensor that cannot confirm a stable flame even when one is present, insufficient or inconsistent gas supply pressure, or a control board that is not sequencing the ignition steps correctly. Because modern gas boilers run through a specific, timed sequence before allowing the burner to fire, a fault anywhere in that sequence, electrical, mechanical, or related to gas supply, can present as the same symptom: the unit tries to light and fails. A licensed gas fitter tests each stage directly rather than guessing which one is at fault.
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Before a gas boiler allows fuel to flow to the burner, its control board runs through a sequence: confirming the venting and any safety switches are satisfied, energizing the igniter, opening the gas valve at the correct moment, and then confirming, through the flame sensor, that a stable flame has actually been established. If any step in that sequence fails or does not confirm within its expected window, the control shuts the gas valve and either retries or moves to a fault or lockout condition depending on how many attempts have failed.
Understanding this sequence is useful because it explains why an ignition failure is not automatically a gas supply problem, or automatically an electrical problem; it could be either, or something in between, and the diagnosis has to isolate which stage actually failed.
| What you notice | Likely stage affected | Notes |
|---|---|---|
| A clicking or sparking sound but no ignition | Igniter or gas valve not delivering fuel at the right moment | Common and usually a straightforward component swap |
| Brief ignition followed by immediate shutdown | Flame sensor failing to confirm a stable flame | Often resolved by cleaning or replacing the sensor |
| No sound or attempt at all | Control board, power supply, or a safety interlock blocking the sequence before it starts | Requires checking upstream conditions first |
| Intermittent success, working some cycles and not others | Marginal gas supply pressure or a sensor on the edge of failing | Worth monitoring pattern and timing to help the technician |
Diagnosis involves testing the igniter's output directly, checking the flame sensor's signal with the appropriate meter, measuring actual gas supply pressure at the unit under load, and reviewing the control board's fault history for a pattern rather than a single event. This is meaningfully different from swapping the most commonly failed part and hoping it resolves the issue, which can leave the true cause, particularly a marginal gas supply, unaddressed and the fault recurring.
In Metro Vancouver, older gas lines feeding multiple appliances in a single home are an occasional contributor to marginal supply pressure, especially where a boiler was added to a home that already had a furnace, water heater, or gas range on the same run, which is exactly the kind of system-level cause a component-only diagnosis would miss.
Safety note
Any diagnosis or repair on a gas-fired boiler must be carried out by a Technical Safety BC licensed gas fitter, since the combustion, venting, and control systems are all connected. If you ever smell gas, hear a hissing sound near a gas line, or notice soot or a burning odour near the unit, leave the home immediately and call FortisBC at 1-800-663-9911 from a safe location.
Not usually. Ignition failure is most often traced to a single component, such as an igniter or flame sensor, and repaired without replacing the unit.
Intermittent ignition failure often points to a marginal condition, such as gas supply pressure near the low end of acceptable, or a sensor that is failing gradually rather than completely, which is worth having tested before it fails outright.
It is possible but less common than an internal cause. A technician measures actual supply pressure at the unit to rule this in or out rather than assuming it.
Many cases are diagnosed and repaired within a single visit once the technician tests the ignition sequence stage by stage, though a marginal gas supply issue can take longer to confirm.
A limited number of attempts is generally fine, but repeated manual restarts without addressing the underlying cause can be counterproductive and, in some cases, mask a safety-relevant fault.
Igniters and flame sensors are wear components that can fail at any age, though a much older unit nearing the end of its service life may show ignition problems alongside other unrelated faults.
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