A tankless unit that fails to ignite in a Port Moody home is missing one of three required conditions: sufficient flow, adequate gas supply, or a working ignition system, and a licensed tech checks each in turn.
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Quick answer
When a tankless water heater won't ignite, the cause is that it hasn't detected enough flow to call for heat, isn't receiving sufficient gas supply, or its igniter and flame sensor aren't completing combustion successfully. Rather than assuming the whole unit has failed, a licensed gas fitter checks flow, then gas supply, then the ignition components themselves to isolate exactly which link broke.
Need a licensed gas fitter for your tankless water heater? Call CANRO at (604) 359-1081 — residential natural-gas heating and hot water across Metro Vancouver since 1999.
Ignition on a tankless unit depends on a short chain of events happening correctly: the unit senses adequate water flow, confirms it has the gas pressure and volume it needs, then fires the igniter and verifies a flame is actually burning through a dedicated flame rod. A single weak link anywhere in that chain results in the same outward symptom, no hot water and no ignition, even though the underlying causes are completely different.
That's why a proper diagnosis works through each step methodically rather than jumping straight to replacing the igniter or gas valve on a guess.
Hillside and character homes around Moody Centre and Heritage Mountain sometimes have gas lines that were sized decades ago for smaller appliances and never reassessed when a higher-output tankless unit replaced an older tank heater, which can leave the unit short on the gas pressure it needs at peak demand. In tighter mechanical closets in newer builds, CANRO also finds flow sensors that have picked up mineral fouling over time and stopped registering an accurate reading.
| Cause | Typical Path |
|---|---|
| Undersized or restricted gas supply | Line sizing assessment and correction |
| Fouled flow sensor | Clean or replace |
| Worn igniter | Replace igniter |
| Failed flame rod | Replace flame rod |
| Aging unit with recurring ignition trouble | Consider replacement, tankless install ballpark $3,500–$7,500, not a quote |
Gas line sizing is worth flagging specifically for older Port Moody homes where a tankless unit replaced a smaller original appliance without the supply line being reassessed at the time.
Safety note
If you ever smell gas, hear a loud bang at ignition, or see the unit shut down repeatedly with a flame or ignition fault, shut off the water heater's gas supply if it's safe to reach and leave the home, then call FortisBC at 1-800-663-9911 from outside. Ignition, burner, and gas valve work must be performed by a Technical Safety BC licensed gas fitter.
You generally can't tell from the outside; a licensed gas fitter measures supply pressure while the unit is under load and compares it against what the manufacturer specifies for that model.
Components like igniters and flame rods wear gradually with use and can fail well after the original install, and flow sensors accumulate mineral deposits over time even on comparatively soft Metro Vancouver water.
One reset attempt following the owner's manual is reasonable. Repeated attempts without understanding the cause risks masking the underlying issue rather than fixing it, and it's better to call a licensed tech after the first failed attempt.
Yes, if a furnace or range is also drawing gas at the same time and the overall supply is marginal, the tankless unit can be the one that comes up short on pressure, especially at peak demand.
A flow sensor problem means the unit never even attempts ignition because it doesn't think water is flowing, while a gas supply issue means it attempts ignition but can't sustain enough flame, which a tech distinguishes by checking each stage separately.
If you smell gas at any point, leave the home immediately and call FortisBC at 1-800-663-9911 from outside rather than continuing to investigate the unit yourself.
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