Scale is mineral deposit that forms inside a tankless unit's heat exchanger as water passes through it, and while Coquitlam's Metro Vancouver reservoir water is soft enough to slow this process considerably, it doesn't stop it, especially on units that have gone many years without a flush.
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Quick answer
Dissolved minerals in water precipitate onto the hot surfaces of the heat exchanger every time the unit fires, and softer water simply has fewer minerals available to deposit compared to harder groundwater sources. In Coquitlam, that means scale-related problems tend to show up later in a unit's life than they would in a harder-water area, which can lull homeowners into skipping maintenance that's still worth doing on a longer timeline.
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Reservoir-fed water is treated to be relatively soft, but it still carries some dissolved minerals, and over enough years and enough gallons through the heat exchanger, that adds up. A unit installed when a Coquitlam home was built a decade or more ago, and never flushed since, can still develop meaningful scale even though the water itself is comparatively gentle.
This is different from areas with harder groundwater, where scale shows up in a matter of a couple of years rather than the better part of a decade, but the underlying mechanism is the same.
Scale insulates the heat exchanger from the water flowing past it, forcing the burner to work harder for the same output temperature, and it narrows the internal passages, which reduces flow. On soft water this tends to show up as a slow, gradual drift in performance — hot water taking a bit longer to reach temperature, or minor fluctuations — rather than a sudden, obvious problem.
A number of older homes in established Coquitlam neighbourhoods have tankless units that were installed at some point and never had a descaling flush, partly because soft water performance issues develop slowly enough that nothing forces the issue. A first-time flush on one of these units, even after many years, often noticeably improves flow and consistency, since there's simply more accumulated deposit to remove than on a unit that's been maintained on a normal schedule.
This process doesn't typically require opening the combustion side of the unit, but the isolation and flush connections are model-specific enough that it's worth having a technician handle it.
| Situation | Suggested flush interval |
|---|---|
| Standard Coquitlam reservoir-fed supply | Every 18–24 months |
| Unit already several years overdue | Book a flush now, then set a regular interval |
| Household with unusually high hot water usage | Closer to the 18-month mark, even on soft water |
Given how much slower scale develops here compared to harder-water areas, the main risk in Coquitlam isn't rapid buildup — it's simply forgetting maintenance for so long that a unit goes a decade without ever being flushed.
Safety note
If you ever smell gas (a sulphur or rotten-egg odour) near your tankless unit, do not flip switches or search for the leak yourself. Leave the house, leave the door open behind you, and call FortisBC at 1-800-663-9911 from outside. Any work on the gas line, venting, or burner assembly has to be done by a Technical Safety BC licensed gas fitter.
Yes, though less often than on hard water — soft water slows scale formation, it doesn't stop it, and a unit several years old without a flush can still have measurable buildup affecting performance.
Gradual changes like a longer wait for hot water to reach temperature, mild fluctuations, or an unusual operating sound during heating are reasonable indicators worth mentioning to a technician.
Given how soft the reservoir water already is, a softener is generally less of a priority here than in harder-water areas, though it remains an option for households wanting to minimize buildup further.
It can still develop enough scale to affect flow and temperature consistency, and in rare cases contribute to reduced heat exchanger lifespan, even though the process moves slowly on soft water.
In most cases a flush meaningfully improves flow and consistency, especially on a long-overdue unit, though a very old heat exchanger with years of accumulated deposit may not return completely to its original output.
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