Ignition failure on a Bosch boiler means the burner did not successfully light within the control board's expected sequence.
Tell us what you need—we’ll call you back fast.
Quick answer
Ignition failure on a Bosch gas boiler occurs when the burner does not achieve a confirmed flame within the control board's ignition attempt window, which can stem from insufficient gas supply, a fouled or misaligned igniter and flame sensor, combustion air or venting restriction, or a control board or wiring fault. The specific cause has to be isolated by a licensed gas fitter using the boiler's diagnostic history and direct inspection, since several unrelated problems can present with the same symptom of repeated failed ignition attempts.
Need a licensed gas fitter for your gas boiler? Call CANRO at (604) 359-1081 — residential natural-gas heating and hot water across Metro Vancouver since 1999.
A Bosch condensing boiler uses an electronic igniter to establish a spark or hot-surface ignition source, opens the gas valve on a precise timed sequence, and then relies on a flame sensor, usually a flame rectification rod, to confirm that combustion actually occurred. If that confirmation does not happen within a few seconds, the control board cuts gas flow and may retry the sequence a limited number of times before declaring an ignition failure and, depending on the model, locking out.
Because this sequence depends on gas supply, spark or surface ignition, proper air mixture, and an accurate flame signal all lining up correctly, ignition failure is one of the more common fault categories technicians see across brands, not something specific to Bosch equipment.
| Category | What It Looks Like | Typical Cause |
|---|---|---|
| Gas supply | Ignition attempted but no flame at all | Low inlet pressure, a partially closed shutoff valve, or an air pocket after gas work nearby |
| Ignition component | Weak or inconsistent spark, or no spark | Worn or fouled igniter, cracked ceramic, or a wiring fault |
| Flame sensing | Flame lights briefly then the board reports failure | Fouled or misaligned flame rectification rod, poor grounding |
| Combustion air/venting | Intermittent failure, worse in wind or cold | Restricted intake or exhaust, condensate blockage in the vent |
| Control board | Erratic behaviour, no clear pattern | Failing board or a loose low-voltage connection |
A licensed gas fitter typically starts by checking incoming gas pressure at the appliance under load, since even a properly sized gas line can show a pressure drop when several appliances run at once in an older home. Next comes a visual and electrical check of the igniter and flame sensor, looking for carbon buildup, cracking, or a signal reading outside normal range with a multimeter.
If the electrical side checks out, attention shifts to combustion air and venting. Sidewall-vented boilers in Metro Vancouver's wetter neighbourhoods can develop condensate pooling or partial ice blockage in the vent run during cold snaps, which restricts the airflow the ignition sequence depends on. On older character homes with a boiler tied into an existing chimney or converted venting arrangement, the technician also confirms the vent configuration itself still matches what the appliance requires.
Only once the mechanical and combustion-air checks are complete does a technician move to control board diagnostics, since board replacement is a comparatively expensive step that should follow, not precede, ruling out simpler causes.
Most ignition failure cases are resolved through targeted component repair: cleaning or replacing the igniter, cleaning or replacing the flame sensor, clearing a vent restriction, or correcting a gas pressure issue upstream of the appliance. These are generally the most cost-effective outcomes and do not require touching the rest of the boiler.
On an older boiler where ignition failures are one symptom among several, including inconsistent heat output, rising service frequency, or a control board that is becoming difficult to source parts for, a technician may raise boiler replacement as a longer-term option, generally in the ballpark of $6,500–$14,000+ for a full install depending on the system's size and complexity, confirmed only after an in-home assessment.
Safety note
If you ever smell gas, hear a hissing sound near the boiler, or a carbon monoxide alarm activates, leave the home immediately and call FortisBC at 1-800-663-9911 from a safe location before doing anything else. Do not attempt to relight, reset, or inspect a gas appliance yourself when a gas odour or CO alarm is involved.
They are related but not identical. Ignition failure describes the specific event of the burner not lighting; if it happens enough times in a row, the control board typically responds by going into a lockout state that requires a reset.
Yes. In older homes with multiple gas appliances running simultaneously, a marginal gas line can show a pressure drop that is enough to interfere with reliable ignition, which a technician can measure directly.
Cold and windy conditions can affect venting performance and combustion air supply, especially on sidewall-vented systems, which is why ignition issues sometimes cluster during cold snaps.
Not necessarily, and it should not be assumed. Ignition and flame-sensing components, gas supply, and venting are checked first since they are more common causes and far less costly to correct than a control board.
This involves accessing the burner assembly on a gas appliance and is not a homeowner task; it should be handled by a Technical Safety BC licensed gas fitter.
If the home still has heat from another source and there is no gas smell, it is not an emergency, but it should be scheduled promptly, particularly heading into colder weather.
Family-run, TSBC-licensed (gas LGA0043870 · boiler LBP0046450), serving Metro Vancouver homes since 1999. Residential, natural gas only.
Call (604) 359-1081 Email info@canroheat.ca“Canro does an amazing job! Super professional and skilled with everything—boilers, furnaces, and AC. Always a pleasure working with them!”
“Five stars for Canro. We needed a replacement of a 30-year-old boiler. A new high-efficiency unit was installed—clean, professional work.”
“I can’t speak highly enough about George, who was recommended for a boiler service call for my parents’ home. George is excellent.”
25+ years keeping Metro Vancouver homes comfortable. Honest advice, upfront pricing, work that lasts.