Repeated ignition failure on a tankless unit is usually a venting, gas supply, or sensor issue rather than a simple pilot light problem.
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Quick answer
Many modern tankless water heaters, including current Takagi models, use electronic ignition rather than a continuously burning standing pilot, so repeated ignition failure typically points to a venting obstruction, insufficient gas supply, a dirty or faulty flame sensor, or a low-voltage power issue rather than a pilot flame simply blowing out. A licensed gas fitter needs to check the actual ignition sequence and venting to identify the real cause safely.
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Whether your specific unit uses a standing pilot or, more commonly on newer tankless models, an electronic ignition system that lights on demand, repeated failure to ignite or stay lit falls into a handful of general diagnostic categories: an ignition problem itself, a flame sensing problem, a venting or combustion air obstruction, a gas supply issue, or a control board or sensor fault. Manufacturers and technicians describe these as categories rather than always pointing to one universal cause, because the actual failure can sit anywhere along that chain.
Never attempt to bypass a safety lockout, hold an igniter open, or repeatedly cycle the unit's reset in hopes it eventually catches. Repeated relighting attempts without diagnosis can mask a venting or gas supply problem that needs to be fixed, not worked around.
| Category | What the Technician Checks |
|---|---|
| Venting and combustion air | Inspects intake and exhaust termination points for blockage or improper clearance |
| Gas supply | Verifies gas pressure and line sizing are adequate for the unit's demand |
| Flame sensing | Cleans or tests the flame sensor, which can cause shutdown even after successful ignition |
| Ignition components | Tests the igniter and ignition control sequence directly |
| Control board and low-voltage wiring | Rules out an electronic fault behind an otherwise normal-looking symptom |
Metro Vancouver's wet, windy winters and the prevalence of exterior-wall tankless venting mean CANRO sees venting-related ignition problems more often here than a dry climate might. Wind-driven rain can occasionally affect a poorly sealed vent termination, leaves and organic debris common in a coastal, tree-heavy region can accumulate at an intake screen, and winter storms can pack snow or ice into a termination point overnight. Character homes with vent runs added during a tankless retrofit are also worth a closer look if the venting was not originally sized or routed with the tankless unit's specific requirements in mind.
Takagi documents general venting and gas supply requirements for its models, but the correct vent length, diameter, and termination clearances depend on your specific installation and should be verified by a licensed technician rather than assumed.
If the unit fails to ignite more than once or twice, or if you smell gas at any point during the process, stop attempting to reset or relight it and call a licensed technician. Repeated ignition failures are the unit's safety systems doing exactly what they are designed to do: refusing to operate under a condition that has not been resolved. Working around that protection rather than fixing the underlying cause is not a safe shortcut.
Safety note
If you ever smell natural gas near the unit or anywhere in the home, leave the home immediately and call FortisBC at 1-800-663-9911 from outside. Do not attempt to relight a pilot, reset an ignition lockout, or open any gas fitting yourself. Gas connections, venting, and combustion-air work on a tankless water heater must be handled by a Technical Safety BC licensed gas fitter; CANRO holds gas licence LGA0043870.
Many current tankless models use electronic ignition rather than a continuously burning pilot; check your specific model's manual, since the diagnostic approach differs slightly.
Yes, a blocked intake or exhaust termination is one of the more common causes of ignition failure, since the unit's safety systems will not allow ignition without proper combustion air and venting.
Repeated reset attempts without diagnosis are not recommended, since they can mask an underlying venting or gas supply problem that needs a licensed technician to identify and fix.
Wind, snow, ice, and debris affecting the vent termination are more common during Metro Vancouver's wet winter storms, which is when CANRO sees more venting-related ignition calls.
Mention any error or lockout indication shown on the unit's display or remote, whether other gas appliances are working normally, and whether the issue seems linked to cold or windy weather.
Yes, a dirty or faulty flame sensor can cause the unit to shut down even after it initially lights, which looks similar to an ignition failure but has a different fix.
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