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Scale from hard water is the most common reason a tankless heater swings in temperature, throws error codes or wears out early. A yearly flush clears it. We service Rinnai, Navien and other major brands across the Westside and central LA.
Hardness is the calcium and magnesium dissolved in your water. When a tankless heater heats it, those minerals come out as scale on the heat exchanger. How fast that happens depends on who supplies your water.
| Area | Supplier and source | Average hardness |
|---|---|---|
| Venice, Mar Vista, West LA, Westwood | LADWP. Mostly Los Angeles Aqueduct water, blended at times with State Water Project water. | 103 mg/L (about 6 gpg) for aqueduct water; blends run higher |
| Hollywood, Silver Lake | LADWP. Aqueduct water, imported water and local wells. | 103–116 mg/L (6–7 gpg) depending on the mix |
| Culver City | Golden State Water. All imported water from the Colorado River and the State Water Project. | 203 mg/L (about 12 gpg), range 137–280 |
| Santa Monica | City of Santa Monica. Up to 75% local wells, softened by reverse osmosis; the rest imported. | See the city’s annual water quality report |
Rinnai’s installation manual lists 200 mg/L as the upper hardness limit for its condensing units, and says hard water areas may need water treatment and more frequent flushing. Culver City’s average sits right at that line.
Figures are 2025 averages from each supplier’s water quality report. 17.1 mg/L equals one grain per gallon (gpg).
We close the service valves under the unit, connect a pump and a bucket of descaling solution to the flush ports, and circulate it through the heat exchanger until the scale dissolves. Then we flush with clean water and reopen the valves.
Swipe sideways to see the whole diagram.
Once a year is our standard schedule. Every system is different, so after the first visit we’ll tell you if yours needs it more often. The annual service and its price are on our Service Agreements page.
Scale on the heat exchanger makes it harder for the unit to hold a steady temperature, especially at low flow.
Due for a flushA clogged inlet screen or a scaled heat exchanger cuts flow. You notice it most in the shower.
Due for a flushRinnai units show an LC code when they detect scale build-up, and some can be set to show a service reminder.
Due for a flushIgnition failures can come from a dirty flame rod, a blocked air intake or a fault that needs repair.
Call usNo symptoms doesn’t mean no scale. It builds slowly until the unit starts complaining.
Book a serviceIf the unit has stopped working, see tankless water heater repair.
Manufacturers treat scale as a maintenance problem, not a defect. Navien’s NPE warranty excludes damage from hard water deposits and lime or mineral build-up, and is void for failure to perform regular maintenance. Rinnai’s installation manual says replacement of components due to water quality damage isn’t covered.
Keep the invoice from every service. If a part fails under warranty, it shows the unit was maintained.
Once a year is our standard schedule, and it suits most homes on LA Aqueduct water. Manufacturers say hard water can call for more frequent flushing, so on the first visit we look at how much scale came out and tell you if your unit needs it sooner.
It depends on your supplier. LADWP’s 2025 report puts its LA Aqueduct water at an average of 103 mg/L of hardness, about 6 grains per gallon. Golden State Water’s Culver City system, which is all imported water, averaged 203 mg/L, about 12 grains per gallon. Santa Monica gets up to 75 percent of its water from local wells and softens it with reverse osmosis. Your utility’s annual water quality report has the exact numbers.
Scale coats the inside of the heat exchanger. It insulates the metal, so the unit works harder to heat the same water, the temperature swings, and hot-water flow drops. Eventually it throws error codes and the heat exchanger can fail. Most manufacturers don’t cover damage caused by scale.
It can. Navien’s NPE warranty excludes damage from hard water deposits and lime or mineral build-up, and is void for failure to perform regular maintenance. Rinnai’s installation manual says replacement of components due to water quality damage is not covered. Keep the invoice from each service in case you ever need to make a claim.
If the unit has service valves, the flush itself is a pump, two hoses and descaling solution, and some homeowners do it. Manufacturers say service should be done by a qualified professional, because the unit runs on gas and electricity. Our service also covers the parts a DIY flush skips: cleaning the inside, the fans, screens and flame rods, and checking for error codes and leaks.
Not cleanly. Without isolation valves there’s nowhere to connect the pump. We can install a service valve kit on the cold and hot lines, which makes this flush and every later one straightforward.
It reduces it. Rinnai’s manual notes that hard water areas may need water treatment as well as more frequent flushing. A softener or scale-reduction cartridge slows the build-up but doesn’t replace the yearly service, and cartridges need changing on their own schedule.
Yes. Our annual tankless water heater service is on the Service Agreements page, with the price and what’s included. We set the schedule for your system after the first visit.
We work from our shop at 5301 Beethoven St in Mar Vista and cover the Westside and central Los Angeles, including Santa Monica, Culver City, Venice, Westwood, Beverly Hills, Hollywood and Silver Lake. We’re open Monday through Saturday 8am to 5pm and Sunday 8am to 4pm. Call (310) 845-6027.
Call our Los Angeles shop to book a service, or ask about the annual plan.
Our plumbing repair solutions are available throughout Los Angeles, including Hollywood, Santa Monica, Beverly Hills, Westwood, Venice, Inglewood, and El Segundo. Wherever you are in the Los Angeles area, we can provide the exceptional plumbing services you deserve!
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