A gas tankless water heater generally benefits from flushing about once a year, though the right interval depends on your specific water hardness and usage — homes on harder well water may need more frequent flushing than homes on the regional soft municipal supply.
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Quick answer
Flushing clears mineral scale from the tankless unit's heat exchanger, which is the same passage the water flows through as it's heated. Left unaddressed, scale reduces heating efficiency and can eventually restrict flow, so the flushing interval matters more for tankless units than it might seem for a small, occasional maintenance task.
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A tankless heat exchanger is a narrow passage that water flows through rapidly while being heated. Mineral content in the water gradually deposits scale on the interior surfaces, similar to how a kettle scales up over time. Flushing circulates a descaling solution through the unit to dissolve that buildup before it affects performance.
| Water condition | Suggested flushing interval |
|---|---|
| Regional soft municipal supply (most Pitt Meadows subdivisions) | Roughly annually |
| Harder well water (some rural or acreage properties) | More frequently, based on water hardness |
| Heavy household hot water use | Closer to annual regardless of water hardness |
Most Pitt Meadows subdivision homes are on the regional Metro Vancouver water supply, which is comparatively soft and generally reduces the rate of scale buildup compared to harder water sources. Rural and acreage properties on private wells can have meaningfully different water hardness, and that difference is worth checking rather than assuming the same flushing schedule applies.
Unlike a tank, which fails gradually as sediment accumulates at the bottom, a tankless unit's performance and lifespan are tied more directly to heat exchanger condition, since there's no separate reservoir to buffer the effect of scale. Regular flushing is a relatively low-cost way to protect a comparatively larger upfront investment.
Many households schedule tankless flushing alongside other annual home maintenance, such as furnace servicing, to keep everything on one predictable schedule rather than tracking separate dates for each system. A technician can usually set this up as a routine visit rather than something you need to remember to book each time.
A technician connects to the unit's isolation valves, circulates a descaling solution through the heat exchanger for a period of time, then flushes it clean with fresh water before restoring normal operation. It's a routine, non-invasive process that typically takes under an hour and doesn't require draining or disturbing the rest of your home's plumbing.
Some older tankless installations were done without dedicated isolation valves, which makes flushing more involved and time-consuming than it needs to be. If your unit doesn't already have them, it's worth having a technician add isolation valves during a service visit — it's a one-time cost that makes every future flush faster and simpler.
A tankless unit that's gone several years without a flush doesn't usually fail outright — it more often shows a gradual decline, with hot water taking longer to arrive and the unit running less efficiently than it used to. Catching up with a flush at that point still helps, though the earlier scale is addressed, the less cumulative strain the heat exchanger has experienced.
Safety note
If you ever smell gas, hear an unusual hissing near the gas line, or suspect a venting or carbon monoxide problem, leave the home immediately and call FortisBC at 1-800-663-9911 from a safe location. Any gas line, venting, or combustion work must be carried out by a Technical Safety BC licensed gas fitter; CANRO holds gas licence LGA0043870 and boiler licence LBP0046450.
Yes, though less urgently than with hard water — even comparatively soft regional water gradually deposits some scale over years, so annual flushing is still generally recommended.
Well water hardness varies by property, so a rural or acreage home may need more frequent flushing than the general annual guideline for municipal water.
Scale gradually builds up in the heat exchanger, reducing efficiency and potentially restricting flow, which can shorten the unit's effective service life.
Longer heat-up times, reduced flow at fixtures, or more frequent fault conditions than usual are all signs it may be time for a flush.
It's generally handled during a professional service visit, since it involves connecting to the unit's isolation valves and running a descaling solution correctly through the system.
Yes — many households bundle tankless flushing with annual furnace or boiler servicing to keep everything on one predictable schedule rather than tracking separate dates.
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