A tankless Noritz unit has no tank to rust, so discoloured hot water usually traces back to home plumbing or the heat exchanger.
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Unlike a storage tank, a Noritz tankless water heater has no large steel tank that can rust from the inside, so discoloured hot water almost always traces back to old galvanized or corroding pipes in the home, sediment stirred up during municipal water main work, or in rarer cases internal corrosion within the unit's heat exchanger or fittings. A homeowner can safely test whether both hot and cold water are affected; anything pointing to the unit itself needs a licensed gas fitter to inspect.
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The classic rusty-water story with a storage water heater is the glass-lined steel tank finally corroding through after years of service, often signalled by rust-coloured water and sometimes a rotten-egg smell together. A Noritz tankless unit doesn't have that large steel tank; water passes through a compact copper or stainless steel heat exchanger only while a tap is open, so the failure mode that produces rust in a tank simply isn't present in the same way.
That means when a homeowner reports rusty hot water from a Noritz unit, the first and most common explanation is upstream of the water heater entirely: the home's own plumbing, particularly if any of it is still galvanized steel, which is common in Vancouver-special and other pre-1970s Metro Vancouver housing stock that hasn't been fully re-piped.
It is uncommon but not impossible for internal fittings, a failing anode-adjacent component on models that use one, or corrosion at brass connections to introduce discolouration into hot water specifically while cold stays clear. If discolouration is isolated to hot water at every fixture in the house and the plumbing has otherwise been updated, that pattern is worth having a technician investigate directly at the unit and its connections rather than assuming it will resolve on its own.
A technician's inspection typically includes checking the inlet water filter or screen, which can trap sediment and occasionally give a false impression that the unit itself is the source when it's really just catching debris already present in the supply.
| Observation | Likely Direction |
|---|---|
| Both hot and cold discoloured at one fixture | Home plumbing near that fixture, or municipal supply |
| Only hot water discoloured, house-wide | Water heater or its connections worth inspecting |
| Clears after running water a few minutes | Often sediment disturbed by nearby work, not a structural issue |
| Reddish-brown and persistent | Iron/rust somewhere in the system; worth tracking down |
Flushing a fixture for a few minutes and re-testing is a reasonable, safe first step. If discolouration persists across multiple days or keeps returning, book an inspection rather than continuing to flush repeatedly.
Safety note
If you smell gas, notice soot around the unit's vent termination, hear a rattling or banging you have not heard before combined with a burning smell, or your carbon monoxide alarm sounds, leave the home immediately and call FortisBC at 1-800-663-9911 from outside before doing anything else. Gas connections, the burner assembly, the heat exchanger, ignition components, and venting on a tankless water heater must only be serviced by a Technical Safety BC licensed gas fitter. CANRO holds gas licence LGA0043870.
Not in the same way; there is no large steel tank to corrode from the inside, so rusty hot water from a tankless unit is more often traced to the home's own plumbing.
If it is isolated to hot water at every fixture, that pattern points toward the water heater or its connections and is worth having a technician check directly.
Occasional sediment-related discolouration is generally not a health concern, but persistent or reddish-brown water should be investigated rather than ignored, especially if you're unsure of the cause.
Yes, nearby main flushing or repair work commonly stirs up sediment that can temporarily discolour tap water throughout a neighbourhood.
If galvanized branch lines are corroding internally, a plumber can advise on targeted repiping; this is a plumbing scope separate from the gas water heater itself.
A basic fixture flush is a reasonable first step, but if discolouration persists, have a licensed technician inspect the unit and its connections rather than repeatedly flushing on your own.
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