Mineral scale builds up inside the RL series heat exchanger over time and a periodic flush is the standard way to keep the unit heating efficiently and firing reliably.
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Quick answer
Descaling a Rinnai RL series unit means circulating a descaling solution through the heat exchanger to dissolve mineral buildup that accumulates from the minerals naturally present in tap water. It's routine maintenance, not a repair, and skipping it for too long is one of the more common reasons these units eventually run into flow or ignition faults.
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Every tankless water heater heats water as it passes through a compact heat exchanger, and the dissolved minerals in that water — mostly calcium and magnesium — precipitate out onto the exchanger's internal surfaces as scale over time. The RL series is a non-condensing tankless unit, so this heat exchanger is the main component doing the work, and scale buildup on it directly reduces how efficiently heat transfers to the water passing through, which is why a scaled unit gradually delivers less hot water at the same flow rate.
Metro Vancouver's municipal water, drawn from the North Shore mountain reservoirs, is relatively soft, so scale accumulates more slowly here than in areas fed by well water or harder municipal supplies. That doesn't mean it never happens — soft water still carries some mineral content, and scale is cumulative over years of operation regardless of how slowly it builds.
A household on well water in the Fraser Valley might need descaling every year, while a similar household on Metro Vancouver's treated reservoir supply could reasonably go two years between flushes with no meaningful difference in performance. The right interval really does depend on the specific water source feeding the home, which is one reason a blanket annual-service recommendation doesn't fit every property equally well.
A technician isolates the unit using its service valves, connects a pump and hose set, and circulates a descaling solution through the heat exchanger for a set period before flushing it clean with fresh water. This is a closed-loop process that doesn't involve draining the home's plumbing or shutting off water to the rest of the house for long. It's a routine maintenance visit, not an emergency repair, and can usually be scheduled in advance rather than reactively.
If your unit doesn't already have isolation valves at the water connections, adding them during the first descaling visit is a one-time step that makes every future flush faster and also makes the unit easier to isolate for any future repair.
Tankless descaling in Metro Vancouver runs $250 to $450 as a 2026 public-market ballpark, not a quote — CANRO's certified technicians confirm the exact cost based on the unit and access. Given the region's soft water, an annual flush is more conservative than most homes strictly need; every one to two years is a reasonable interval for most households, with harder-water properties or high-usage homes benefiting from more frequent service.
Safety note
Descaling involves isolating a gas-fired appliance and working near its water and combustion connections, so it should be done by a licensed technician rather than attempted with improvised equipment. If you ever smell gas while a technician is on site or at any other time, leave the house and call FortisBC at 1-800-663-9911.
Some homeowners with the right equipment and isolation valves already installed do attempt this, but incorrect connection or solution handling can damage the heat exchanger, so most homeowners have a licensed technician perform it.
Manufacturer warranty terms vary and change, so check your certificate — but skipping maintenance can affect a warranty claim if scale is found to be the cause of a failure.
If the lockout is caused by restricted flow from scale, yes; if it's an ignition or venting fault, descaling won't resolve it and a full diagnostic is needed instead.
No — soft water slows scale buildup but doesn't stop it, and skipping maintenance indefinitely still shortens the unit's service life.
A standard flush is typically completed within a single visit, though exact timing depends on unit access and whether isolation valves are already in place.
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