Professional descaling for a tankless water heater runs about $150 to $350 a visit, average near $200 to $250, according to 2026 cost data from HomeGuide and Angi. A reusable DIY descaling kit costs $100 to $300 up front, with each additional flush needing only $10 to $20 in vinegar or descaling solution.
Hot Water Brief is an independent cost-research site. We are not a contractor and do not perform the work ourselves.
Maintenance is priced differently from repair or replacement. The table below lines up the published ranges, each with a source and a date.
| Maintenance item | Published range | Typical | Source and date |
|---|---|---|---|
| Professional tankless descaling | $150 to $350 | about $250 | HomeGuide, 2026 |
| General water heater flush and clean, tank or tankless | $169 to $386 | about $278 | Homewyse, January 2026 |
| DIY descaling kit, pump, hoses and bucket | $100 to $300 | about $175 | Angi, 2026 |
| DIY descaling solution or vinegar only, kit already owned | $10 to $20 | about $15 | HomeGuide, 2026 |
None of these figures is a quote for your unit, and only a licensed local company that has looked at it can price the job. For repair and replacement figures, see the cost breakdown.
Navien recommends descaling a tankless water heater at least once a year, and Noritz ties the same interval to preventing its scale related error code. Both manufacturers say hard water shortens that interval. Navien states owners with hard water may need to service the unit more often than the standard annual schedule.
The two manufacturers frame the same warning differently. Navien's descaling guide, published May 2, 2023, states it recommends descaling a tankless water heater at least once a year, adding that frequency varies with mineral content, temperature setting and hot water usage. Noritz documents its own scale related fault, error code 16, and says annual descaling or a water softener prevents it.
Hardness itself has a published scale. The U.S. Geological Survey classifies water above 180 milligrams per liter as calcium carbonate as very hard, against 0 to 60 for soft water, with moderately hard and hard water in between. Neither manufacturer publishes an exact hardness threshold in grains that shortens the interval, so treat any specific number attached to hard water servicing as unsourced unless the source is named.
Filter cleaning does not carry its own published national price, because manufacturers bundle it into the same annual visit as descaling. The Department of Energy's Building America Solution Center recommends cleaning a tankless unit's water and air filters every 6 to 12 months, and warns that a clogged air filter stops the unit from working until it is cleaned.
Navien's own annual maintenance list, published November 26, 2024, groups the inlet water filter, the intake air filter and the condensate trap into the same visit as the heat exchanger flush and a visual inspection, rather than pricing filters as a separate job. Practically, the $150 to $386 range in the table above already covers filter cleaning when a professional does the work.
For a homeowner doing it without a technician, cleaning the filters is closer to free. Navien's guidance describes rinsing and scrubbing the inlet water filter and cleaning the air intake filter with a toothbrush, tools most households already own.
On Rinnai condensing units, a dirty air filter or frozen condensate line can trigger Rinnai code 10.
Skipped maintenance lets mineral deposits coat the heat exchanger, which Navien says reduces efficiency and, along with buildup in the pipes and filter, reduces water flow. Left long enough, scale trips Noritz's error code 16 and can turn into a $150 to $450 repair, and it is also the exact failure mode Rheem's warranty does not cover.
Navien's maintenance guide, updated November 26, 2024, lists three consequences of skipping the annual visit: mineral deposits on the heat exchanger that reduce efficiency, mineral buildup in the pipes and filter that reduces water flow, and a shorter service life. It adds that damage from not following the manual's maintenance requirements can itself be grounds for a denied warranty claim.
Rheem's residential tankless warranty document makes the same point from the other direction, excluding damages, malfunctions or failures caused by lime, mineral buildup or scale, the same failure a routine descaling prevents. A skipped visit can end up costing both the repair and the warranty protection that would otherwise have paid for it. See the problems guide for diagnosis of error codes.
| Scenario | Published range | Typical | Source and date |
|---|---|---|---|
| Skipped maintenance, scale or clog repair | $150 to $450 | about $300 | Fixr, tankless repair cost, published January 31, 2025 |
| Warranty claim for scale damage | Excluded from coverage | not applicable | Rheem residential tankless warranty, document AP21265 Rev 03 |
Rheem's troubleshooting manual lists dirty burners, fans and vents among the causes of Rheem tankless code 13. Rheem asks owners to clean the inlet water filter monthly; a clogged one is a common cause of the Rheem P1 code. A blocked or badly cleared vent terminal is one of the listed causes of Rinnai code 12, Flame Failure.
Navien publishes its own DIY descaling steps, using a submersible pump, hoses, a bucket and either an approved descaling solution or household white vinegar circulated for at least 45 minutes. Despite publishing the steps, Navien states it recommends hiring a professional, and warns that damage caused by an incorrect DIY descaling can void the warranty.
The trade off is mostly financial against risk. A reusable descaling kit costs $100 to $300, after which each flush needs only $10 to $20 in solution or vinegar. Angi's 2026 estimate frames the gap as up to $100 saved per visit by doing the work yourself.
What that comparison leaves out is the warranty language above. For a unit still inside its parts or heat exchanger coverage, the deciding question is not whether $100 is worth saving. It is whether that saving is worth risking coverage on a part that costs far more than $100 to replace.
Every figure on this page traces to a published, dated source, listed below with its date. Manufacturer maintenance and warranty guidance comes from Navien, Noritz and Rheem directly rather than from a summary, and the cost ranges come from separately dated 2026 cost calculators and guides.
Prices move, so check the dates above against the day you are reading this.
HomeGuide's 2026 data puts professional tankless flushing at $150 to $350 a visit, and Angi's 2026 estimate puts it at $150 to $250. Homewyse's broader cleaning calculator, dated January 2026, gives $169 to $386 for tank and tankless units together. A DIY kit runs $100 to $300 up front, with refills at $10 to $20.
At least once a year, according to both Navien and Noritz. Navien's descaling guide, published May 2, 2023, recommends annual service and notes frequency varies with mineral content and usage. Noritz ties the same annual interval, or a water softener, to preventing its own scale related error code 16.
Navien publishes the steps: a submersible pump, hoses, a bucket, and a descaling solution or white vinegar circulated for at least 45 minutes, then flushed with fresh water. Despite publishing that guide, Navien recommends hiring a professional and warns that damage from an incorrect DIY descaling can void the warranty.
Navien lists mineral deposits on the heat exchanger reducing efficiency, buildup in the pipes and filter reducing water flow, and a shorter service life. Noritz's error code 16 is the unit reporting the same scale problem, and Fixr's tankless repair guide, published January 31, 2025, prices a clog or scaling repair at $150 to $450.
It can. Rheem's residential tankless warranty document excludes damages, malfunctions or failures caused by lime, mineral buildup or scale, which is the exact damage routine descaling prevents. Navien separately states that damage from not following the manual's maintenance requirements can itself be grounds for a denied claim.
Every 6 to 12 months, according to the Department of Energy's Building America Solution Center, updated July 22, 2025. It warns that a clogged air intake filter stops the unit from working until it is cleaned, and manufacturers such as Navien bundle filter cleaning into the same annual visit as descaling.
Independent Research
Published ranges for tank and tankless replacement, the failures that justify a repair, and the ones that do not. Sourced, dated, and free to read.
