A Bosch tankless water heater pilot or ignition that keeps failing usually points to venting, gas supply, or a sensing component, not a simple reset fix.
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Quick answer
A Bosch natural-gas tankless water heater that keeps losing its pilot or fails to sustain ignition is most often caused by a venting or air-supply restriction, insufficient gas pressure or flow, a dirty or failing flame sensor, or a draft affecting combustion air. Because most modern Bosch tankless units use direct electronic ignition rather than a standing pilot, a Technical Safety BC licensed gas fitter should diagnose the ignition and sensing components directly rather than repeatedly relighting it.
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Many homeowners use "pilot light" as shorthand for any ignition problem, but most modern Bosch tankless water heaters use direct electronic ignition, lighting the burner on demand rather than keeping a small standing flame running continuously. If your unit repeatedly fails to ignite, fails partway through a shower, or shows an ignition-related fault indicator, the underlying causes overlap closely with classic pilot problems: something is interrupting either the spark/ignition sequence or the flame-sensing feedback that tells the control board combustion is happening safely.
Because tankless units are more electronically dependent than older standing-pilot tanks, troubleshooting usually involves the control board's fault history in addition to the physical components a technician inspects.
Tankless water heaters draw much more combustion air per minute than a standard tank when firing at full demand, which makes correct vent sizing, length, and termination clearance especially important. A vent termination that has been partially blocked by debris, snow, vegetation growth, or even a bird's nest can starve the unit of intake air or restrict exhaust, both of which can trigger ignition lockouts as a safety measure. Homes in exposed or hillside locations around Metro Vancouver can see more wind-related draft effects at the vent termination than more sheltered locations.
| Area Checked | What It Reveals |
|---|---|
| Vent intake/exhaust termination | Blockage, improper clearance, or wind/draft interference |
| Gas supply pressure and line sizing | Whether the unit is getting adequate, stable gas flow |
| Flame sensor condition | Corrosion or misalignment causing false shutdowns |
| Igniter and control board fault history | Recurring lockout codes pointing to a specific component |
| Combustion analysis | Whether the burner is firing cleanly and completely |
An isolated flame sensor or igniter issue on an otherwise well-functioning Bosch tankless unit is a straightforward, worthwhile repair. Recurring lockouts tied to inadequate gas supply usually mean the gas line, not the water heater, needs attention, which a licensed gas fitter can assess and correct. If a unit has a history of multiple different faults, or the control board itself is failing, a technician can help weigh the cost of repeated repairs against replacement.
Do not attempt to clear a vent termination, adjust gas pressure, or bypass a safety lockout yourself. If you ever smell gas near the unit, leave the home immediately and call FortisBC at 1-800-663-9911 from a safe location. All gas appliance diagnostic and repair work in BC must be performed by a Technical Safety BC licensed gas fitter; CANRO holds gas licence LGA0043870 and boiler licence LBP0046450.
Safety note
Venting, gas supply, and ignition component work on a tankless water heater must only be performed by a Technical Safety BC licensed gas fitter. If you smell gas, leave the home and call FortisBC at 1-800-663-9911.
Most modern Bosch tankless models use direct electronic ignition rather than a continuously burning pilot, so ignition failures show up as the unit not firing or dropping out mid-use rather than a visible pilot flame going out.
Yes. Wind and cold can affect draft at an exposed vent termination, and Metro Vancouver's damp coastal climate and occasional cold snaps are a recognized factor in venting-related ignition issues on exterior-wall installs.
Repeatedly resetting a unit that keeps locking out is not a fix and can mask a venting or gas supply problem that needs proper diagnosis. Have a licensed gas fitter check it if the issue recurs.
Yes, especially in homes with multiple gas appliances sharing a line. Tankless units draw more gas at full demand than a standard tank, so line sizing and pressure are common checkpoints.
It confirms to the control board that the burner has actually ignited. If it is dirty, misaligned, or failing, the board may shut the burner down as a safety precaution even when ignition briefly succeeded.
If a technician finds recurring, unrelated faults or a failing control board on an older unit, replacement can be more cost-effective than repeated repairs. A licensed assessment can guide that decision.
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