Ignition failure in an HTP boiler means the unit attempts to fire but cannot confirm a flame, and the cause needs proper diagnosis rather than repeated resets.
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Quick answer
Ignition failure in an HTP gas boiler means the control system attempted to establish a flame but could not confirm it within the expected window, most commonly due to a fouled or misaligned flame sensor, a weak igniter, insufficient gas supply, or a fault in the ignition control board. A licensed gas fitter diagnoses this by testing each component in sequence rather than guessing, since several different faults can produce the same symptom.
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Ignition failure typically shows up as the boiler attempting to start, sometimes with an audible click or spark, followed by a lockout indicator on the display rather than the burner staying lit. Some units will try a few times before locking out, while others lock out after a single failed attempt, depending on the model's programming.
This is different from a boiler that never attempts to start at all, which usually points toward a thermostat or power supply issue rather than a true ignition fault, since ignition failure specifically means the boiler tried to fire and failed to confirm a flame.
A fouled or corroded flame sensor is one of the most frequent causes, since the sensor's job is to confirm a flame is actually present, and a dirty or misaligned sensor can fail to detect a flame that is genuinely burning normally. A weak or degraded igniter may not produce enough spark or heat to light the burner reliably, especially as it ages.
Gas supply issues, including a partially closed manual shutoff valve, low incoming gas pressure, or air in the line after work on the gas piping, can also prevent successful ignition. Less commonly, a fault in the ignition control board itself can cause it to misfire the sequence even when the sensor and igniter are both in good condition.
In some installations, a draft disturbance at the moment of ignition, caused by wind conditions at an exterior vent termination or a partially restricted vent, can blow out a newly established flame before the sensor confirms it, which then registers as an ignition failure even though the igniter and sensor are both functioning correctly. This is worth considering in exposed installations, including many North Shore and hillside homes where wind loading on exterior walls is more pronounced.
Because several different faults can produce an identical symptom on the display, a technician typically works through gas supply, sensor condition, igniter condition, and venting in a logical sequence rather than replacing parts on a guess.
| Step | What is checked | What it rules in or out |
|---|---|---|
| Gas supply | Manual valve position, incoming pressure | Fuel delivery to the burner |
| Flame sensor | Cleanliness, position, signal strength | Whether a real flame is being detected |
| Igniter | Spark or hot-surface output | Whether ignition source is strong enough |
| Venting and draft | Termination clearance, inducer operation | Whether the flame is being disturbed |
| Control board | Sequence timing, output signals | Whether the board itself is misfiring the sequence |
Diagnosing and correcting ignition failure involves working directly with gas supply components, the ignition system, and combustion safety devices, all of which require a Technical Safety BC licensed gas fitter both by law and for genuine safety reasons. A component that appears to fix the symptom when swapped without proper diagnosis can leave an underlying gas supply or venting issue unresolved.
The one thing a homeowner can reasonably check is whether the manual gas shutoff valve near the boiler is fully open, since this is occasionally the simple explanation after unrelated work near the gas line. Beyond that, repeated ignition attempts without a proper diagnosis should be avoided.
Safety note
If the boiler smells of gas during or after an ignition attempt, or you hear hissing near the gas line, leave the home immediately and call FortisBC at 1-800-663-9911 from a safe location. Diagnosis and repair of ignition failure must be carried out by a Technical Safety BC licensed gas fitter; do not attempt to service the gas valve, igniter, or flame sensor yourself.
Ignition failure means the boiler attempted to fire but could not confirm a flame, while a boiler that never attempts to start usually points to a thermostat or power supply issue instead.
Yes, a fouled or misaligned flame sensor can fail to detect a flame that is genuinely burning, causing the control system to assume ignition failed and lock the boiler out.
In exposed installations, wind at an exterior vent termination can occasionally disturb a newly lit flame before the sensor confirms it, registering as an ignition failure even though the components are working correctly.
Confirming the manual gas shutoff valve near the boiler is fully open is a reasonable check, especially after any unrelated work near the gas line; beyond that, diagnosis should be left to a licensed technician.
Several different issues, including the sensor, igniter, gas supply, and venting, can all produce the same ignition failure symptom, so a logical diagnostic sequence is needed to identify the real cause.
Repeated reset attempts after ignition failure are not recommended, since each attempt is another ignition sequence under conditions the boiler has already flagged as unsafe or abnormal.
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