Carbon buildup on a flame sensor's tip is one of the most common reasons its signal weakens, often solvable with a simple cleaning.
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Quick answer
A boiler flame sensor is replaced once a technician tests its microamp signal during a live burn and finds it below the manufacturer's minimum even after cleaning carbon buildup from the tip. The classic symptom is a boiler that ignites briefly then locks out on flame loss. In Coquitlam, this shows up across both older and newer boilers regardless of neighbourhood. Cleaning or replacing a flame sensor is typically a short, same-visit repair.
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A failing flame sensor on a gas-fired boiler usually shows up as one or more of the following.
Before replacing a flame sensor, a licensed technician tests its signal directly and tries cleaning first.
| Symptom | Likely cause |
|---|---|
| Ignites, runs briefly, shuts down | Flame sensing fault, sensor or its wiring |
| Marginal microamp reading | Carbon buildup, try cleaning first |
| Very low or no signal even when clean | Sensor replacement needed |
| Signal fine but still locks out | Look at ignition or gas valve instead |
A flame sensor works by detecting a tiny electrical signal called flame rectification, and carbon buildup on the sensor tip is one of the most common reasons this signal weakens over time, often solvable with a simple cleaning rather than a full replacement. When cleaning doesn't restore an adequate reading, though, replacement is the reliable next step rather than repeated cleaning attempts.
Coquitlam's damp coastal climate, similar to the rest of Metro Vancouver, means condensation and humidity in an unheated garage or crawl space mechanical room is a routine factor a technician checks during any service call. That backdrop is relevant to a flame sensor because it shapes what a technician expects to find before ever opening the unit.
Large stretches of Burke Mountain and Westwood Plateau were built out from the 2000s onward, and these newer homes typically run high-efficiency condensing equipment with plastic venting rather than the masonry chimneys seen on older streets. If a flame sensor has failed more than once on the same system, it is worth asking a Coquitlam technician to look at the broader installation rather than treating each failure in isolation.
Safety note
This is gas-fired heating equipment, so any work touching the venting, control, or combustion path must be done by a Technical Safety BC licensed gas fitter; CANRO holds gas licence LGA0043870 and boiler licence LBP0046450. If you ever smell gas near the boiler, leave the home immediately and call FortisBC at 1-800-663-9911 before doing anything else.
Often yes, light carbon buildup can be cleaned off the sensor tip and restore a normal signal without needing a new part.
This flame-loss lockout pattern is a classic sign of a flame sensing fault, where the control can't confirm the flame is actually burning even though it briefly ignited.
It's the safety system doing exactly what it should, shutting off gas flow when flame can't be confirmed, but the underlying sensor issue still needs to be diagnosed and fixed.
Cleaning or replacing a flame sensor is typically a short, same-visit repair.
It can recur if carbon buildup returns, which is why persistent cases often lead a technician to recommend replacement instead of repeated cleaning.
Repeatedly resetting a boiler that keeps locking out isn't a good long-term approach; it should be diagnosed by a licensed technician rather than reset indefinitely.
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