Hot water that surges hot and cold in a New Westminster home with a tankless unit often points to a failing flow sensor, not the burner.
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Quick answer
Replacing the flow sensor on a gas tankless water heater in New Westminster typically costs $250-$900 for the part and labour, plus a $90-$150 diagnostic call and $95-$165 hourly labour if billed separately. That's a 2026 ballpark from public market data, not a quote — CANRO's certified technicians confirm the exact figure once they've checked the sensor's reading against actual measured flow.
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A tankless unit doesn't heat a fixed volume of stored water — it has to detect flow the instant a tap opens and modulate the burner in real time to match. The flow sensor, usually a small turbine or paddle wheel at the cold-water inlet, is what tells the control board exactly how much water is moving through the unit so it can calculate the right burner output. Get that reading wrong, even slightly, and the unit either overshoots or undershoots the target temperature.
A failing or fouled flow sensor typically causes noticeable temperature swings during use — water that surges hotter or colder without you touching the tap, or a unit that won't fire at all at very low flow rates because it can't confirm the minimum activation flow.
| Item | Typical range |
|---|---|
| Flow sensor replacement (part + labour) | $250-$900 |
| Diagnostic/service call | $90-$150 (credited toward the repair) |
| Technician labour, if billed hourly | $95-$165 per hour |
A sensor that just needs cleaning of mineral or sediment buildup, rather than full replacement, often costs less than this range. Full replacement is needed when the turbine itself is physically worn or the sensor housing has cracked.
A flow sensor issue is a contained, worthwhile repair and not a sign the tankless unit itself needs replacing — it's a small sensing component, separate from the heat exchanger and burner that do the actual work of heating. It's worth pairing this repair with a check of the inlet filter and a general flush, since sediment reaching the flow sensor usually means sediment is reaching other internal components too.
Metro Vancouver's generally soft, reservoir-supplied water — which covers most of New Westminster — means sediment problems here are more often about municipal line debris or age of the plumbing than mineral scale specifically, which is a slightly different maintenance conversation than in harder-water regions of the Fraser Valley.
Safety note
If you ever smell gas, hear hissing at a gas fitting, or a carbon-monoxide alarm sounds, leave the home immediately and call FortisBC's emergency line at 1-800-663-9911 from outside before doing anything else. Any work on the gas line, gas valve, or venting on this appliance must be done by a Technical Safety BC licensed gas fitter; CANRO holds gas licence LGA0043870 and boiler licence LBP0046450.
Unpredictable temperature swings during steady use, without touching the tap, are a common flow sensor symptom on tankless units, since the burner is reacting to a flow reading that's no longer accurate.
Yes, if the issue is buildup rather than physical wear on the turbine, cleaning can restore accurate function and avoid a full replacement.
Tankless units require a minimum flow rate to activate, and a fouled or miscalibrated flow sensor can push that threshold higher than it should be, causing the unit to ignore genuinely usable flow.
They're separate parts, but they're both affected by the same sediment moving through your water supply, so a technician often checks both during the same visit.
It can reduce sediment reaching the unit, but it's a separate investment decision from this specific repair, and your technician can advise whether it makes sense for your situation.
Most are completed within an hour or two once the diagnosis confirms the sensor, rather than something else, is the cause.
It can help by cutting down on sediment reaching the unit, though it doesn't replace the need for periodic checks, since some fine debris still gets through most residential filtration setups.
Not directly — that delay is mostly about the distance of pipe between the unit and the fixture, though a malfunctioning sensor can affect how smoothly the temperature stabilizes once flow begins.
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