A flow sensor problem in Surrey often looks like a mystery no-hot-water call, since the rest of the tankless unit tests out fine.
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Quick answer
Replacing a flow sensor on a residential tankless water heater in Surrey generally costs $250 to $900, the standard tankless repair range, plus the $90 to $150 service call, based on 2026 public market pricing rather than a fixed quote. Because a weak flow signal can also come from a clogged inlet filter rather than the sensor itself, CANRO's technicians confirm the actual cause, and the cost, after testing your specific unit.
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A tankless water heater only fires its burner when it detects water moving through the unit at or above a minimum flow rate, and that detection comes from a small turbine or paddle-wheel flow sensor mounted in the cold water inlet. Open a tap, water moves, the sensor spins, and the control board interprets that spin rate as a signal to start the ignition sequence. Below the minimum threshold, often triggered by a single slow-running fixture, the unit simply won't fire, which is normal behaviour rather than a fault.
When the sensor itself degrades or its impeller gets fouled, the unit can misread actual flow, either failing to fire when it should, or firing inconsistently and producing water temperature that swings instead of holding steady.
A genuinely bad flow sensor and a sensor that's simply reading low because of upstream debris, mineral scale, or a partially closed isolation valve can look identical from a homeowner's perspective: inconsistent hot water or the unit not firing on low-flow fixtures. A technician typically checks the inlet filter and isolation valves before condemning the flow sensor itself, since replacing the sensor won't fix a flow problem that's actually caused by something feeding into it.
Homes across Surrey with older galvanized supply piping, more common in some pre-1990s properties before copper and PEX became standard, can shed small amounts of internal corrosion that lodge in a flow sensor's impeller over time.
| Line item | Typical range |
|---|---|
| Diagnostic / service call | $90 – $150 |
| Flow sensor replacement (parts + labour) | $250 – $900 (typical tankless repair range) |
| Inlet filter cleaning, if that's the actual cause | often included in the same visit or billed at the lower end of the range |
A flow sensor problem is a routine repair on an otherwise sound tankless unit and rarely points to needing a whole new heater. Where it's worth a broader look is on an older unit with a documented history of sediment or scale issues, since a technician may recommend a more thorough internal flush alongside the sensor replacement to prevent the same problem recurring.
Safety note
A flow sensor issue on its own isn't a combustion safety concern, but any work inside a gas-fired tankless unit's water and control connections should be done by a licensed gas fitter. If you ever notice a gas smell near the unit, leave the home and call FortisBC at 1-800-663-9911.
Most tankless units require a minimum flow rate to trigger ignition, so a very low-flow fixture may simply not draw enough water to activate it. This is normal design behaviour, though a technician can check whether your unit's threshold matches its specification.
Yes, and it's one of the first things checked, since restricted flow from a clogged filter can produce the same inconsistent firing or reduced hot water that a failing flow sensor causes.
A straightforward swap typically takes under an hour, though the visit may run longer if the technician also needs to flush the inlet filter or check isolation valves as part of confirming the cause.
Scale and sediment can foul the sensor's small impeller over time, especially in homes with older piping or during periods of construction nearby that stir up sediment in the municipal supply.
It can, if the sensor was the actual cause. Inconsistent temperature can also come from a scaled heat exchanger or a mixing valve issue, so a technician usually checks more than one component before concluding it's the flow sensor.
That depends on the manufacturer and how old your unit is, so it's worth checking your original installation paperwork or warranty certificate before booking a paid repair.
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