Annual tankless maintenance is one visit a year that covers more than the flush. A technician descales the heat exchanger, cleans the cold-water inlet filter, looks at any codes the heater has shown, replaces a scale-prevention cartridge if one is fitted, and checks the venting and combustion air. Takagi’s manual recommends having the unit checked once a year by a licensed technician, and Navien recommends descaling at least once a year.
What a yearly visit covers
Flush and descale
This is the center of the visit. The technician closes the isolation valves (the service valves on the water lines), circulates vinegar or descaler, rinses and restarts. The flush and descale page compares each brand’s procedure in a table.
Inlet water filter
Tankless heaters have a small screen where cold water enters. It catches grit and flakes of scale before they reach the heat exchanger. Navien’s procedure says to remove the cold water inlet filter and clean out any residue. A clogged screen starves the heater of flow. Navien even lists cleaning the inlet filter as a fix for E030, which it describes as exhaust overheating.
Codes and the display
Tell the technician about any code you’ve seen since the last visit, even one that cleared on its own. Some codes let the heater keep working. Rinnai notes that LC is the only code that lets the unit keep running, so it’s easy to ignore. If your model keeps a stored list of past codes, its manual explains how to read it. The error code hub explains what the common ones mean.
Scale-prevention cartridge, where fitted
Some homes have an inline cartridge that slows scale. Rinnai says most homes need a new cartridge for its Scale Control System every 10 to 12 months. On Rheem RTGH heaters, code 88 is a reminder to flush the heat exchanger and/or replace the water treatment filter, so the same reminder can cover both jobs. See scale prevention for how these systems compare with a softener.
Venting, combustion air and condensate
Gas tankless heaters pull in air and push out exhaust through vent pipes. Only a technician should check or work on them. Two manufacturer codes show why the check matters. Rinnai lists code 10 as an air supply or exhaust blockage, and its manual adds a full condensate trap as a cause. Noritz lists code 90 as a possible blocked air supply or exhaust vent, abnormal combustion, or a clogged condensate drain.
Condensing models, the high-efficiency type, also make condensate: water that drains away through a trap and a drain line. What gets checked there, and how often, is set out in your model’s manual.
Reminder settings built into your heater
Most current heaters can nag you when service is due. A technician usually sets the reminder from an installer menu.
- Rinnai SENSEI: the Service Soon (SS) reminder can be set to every 6 months, 1 year or 2 years (installer-selected), or turned off, based on water conditions.
- Navien NPE-2: the descaling reminder can be set to no alarm, 6, 12 or 24 months. When it’s due, the heater shows E760.
- Rheem RTGH: the maintenance notice is off by default. It can be set to remind you after 500, 750 or 1,000 hours of operation, measured in burner run time.
- Noritz EZ: Noritz calls for periodic flushing in hard-water areas. Its optional C1# code is a service reminder for periodic maintenance, such as flushing scale from the heat exchanger.
Ask the technician to set the reminder to match your water, not just the factory default. A home on Highland’s 14 gpg well water is in a different spot from one on Saratoga Springs water averaging 8.3 gpg.
How often each brand says to service
| Brand | What the manufacturer says | Built-in reminder |
|---|---|---|
| Navien | descale at least once a year; with no treatment device, flush once a year (twice a year for very hard water in commercial use) | descale reminder, shown as E760 |
| Rinnai | in hard-water areas, the water must be treated and may require a more frequent flushing schedule | SS (SENSEI), set to every 6 months, 1 year or 2 years (installer-selected) |
| Noritz | periodic flushing in hard-water areas | C1# service reminder (optional) |
| Rheem | flush the heat exchanger regularly | maintenance notice after 500, 750 or 1,000 hours of operation; code 88 |
| Takagi | checked once a year; periodic flushing by a plumber in exceptionally hard water | none named in our sources |
| Bosch | descale periodically, where water is highly mineralized | none named in our sources |
The cost guides lean shorter. HomeGuide suggests every 6 to 9 months in homes with hard water. The flush interval guide works through hardness, softeners and household size.
Why it matters for your warranty
Manufacturers don’t cover damage that scale causes, and most Wasatch Front water makes scale. The exclusions, in their own words:
- Navien: hard water deposits and lime or mineral build-up are excluded.
- Rheem: damage caused by lime, mineral build-up, or scale is excluded.
- Noritz: problems resulting from scale formation are not covered.
- Bosch: damage from scale/mineral deposits is not covered.
- Takagi, for single-family homes: hard water above 7 gpg (120 ppm) is excluded.
None of these say a yearly visit guarantees coverage. What the visit does is keep scale from building up enough to cause the kind of failure these warranties exclude. Keep the technician’s dated invoice with your heater’s paperwork. The warranty and scale guide goes through each brand’s terms.
The Department of Energy makes the same point more broadly. It says periodic maintenance can significantly extend your water heater's life and limit lost efficiency.
What yearly maintenance costs
HomeGuide’s maintenance cost guide gives these averages:
| Item | HomeGuide range |
|---|---|
| Yearly maintenance, gas tankless | $150–$650 |
| Yearly maintenance, electric tankless | $150–$600 |
| Flush on its own | $150–$350 |
| Minor repairs found during a visit | $50–$300 |
The yearly maintenance ranges include flushing, filter replacement and minor repairs, which is why they run higher than a flush alone.
We don’t sell a maintenance plan. Some local technicians offer yearly or multi-year pricing, and each sets their own terms. When you book, ask what a repeat visit costs, whether a cartridge is included, and whether they’ll remind you when the next one is due.
Where yearly service matters most
Hardness varies a lot across the area. Spanish Fork’s city page listed 13.4–20.24 gpg, and Herriman says its local wells run 25–60 gpg. Homes on water like that are good candidates for a shorter interval. Water in Riverton and South Jordan comes from Jordan Valley Water Conservancy District and sits lower, but it still reaches or passes the limit Takagi sets. Your city page lists the local figure and who supplies your water.