If you’ve ever pulled a glass out of the dishwasher and found it coated in chalky white film, you already know what Orange County water does to surfaces. That same mineral load (calcium and magnesium dissolved in water drawn from the Colorado River and Northern California aqueducts) is working through your tankless water heater every time hot water runs. The difference is you can’t see it happening until something breaks.
At Comfort Air, we’ve been servicing water heaters and plumbing systems in this area since 1993, and hard water damage to tankless units is one of the most consistent problems we see. Most homeowners don’t realize how much their city’s specific water hardness changes the maintenance math, or what’s actually at stake when that maintenance gets skipped. The answers are more concrete than most online advice lets on.
Why Hard Water Hits Tankless Units Harder in Orange County
A tankless water heater works by passing cold water through a heat exchanger (a coiled tube exposed to a high-output burner) and delivering hot water instantly on demand. That design is efficient precisely because the heat exchanger has a large surface area in direct contact with water, and that’s also exactly why limescale accumulates so aggressively inside it. When hard water is heated, dissolved minerals precipitate out of solution and bond to metal surfaces. As little as an eighth of an inch of buildup can cut heat transfer efficiency by 20 to 25 percent, which means the unit works harder, burns more fuel, and delivers less hot water.
The Irvine Ranch Water District classifies water at 10 or more grains per gallon (GPG) as hard. GPG is the standard unit for measuring water hardness: one grain per gallon equals roughly 17.1 milligrams of calcium carbonate per liter. Water imported into Orange County from the Colorado River and Northern California tends to fall firmly in the hard range, while locally sourced well water is only moderately hard. Your home’s water source determines which number actually applies to your tankless unit.
The range across Orange County cities tells a story that a single blanket recommendation can’t capture. Municipal water quality reports show Anaheim running between 15 and 19 GPG, Huntington Beach at 17 GPG, and the El Toro Water District serving Lake Forest at 18 GPG. Fountain Valley and Costa Mesa run lower, at 12 to 15 GPG. These aren’t trivial differences. A unit on Anaheim tap water is dealing with roughly 50 percent more mineral load than the same unit in a softer-water city. The right maintenance schedule has to reflect that.
The Warranty Threshold Most Homeowners Never See
Most tankless water heater warranties have an exclusion that almost nobody reads until it’s too late. Noritz’s published limited warranty explicitly excludes damage from water with hardness levels above 12 grains per gallon (200 mg/L). That’s not vague language about “scale damage” as a general category. It’s a specific number written directly into the warranty terms.
Look back at the city data above. Anaheim, Huntington Beach, and Lake Forest all exceed 12 GPG. Homeowners in those cities running unsoftened tap water through a Noritz unit are already operating above the threshold the manufacturer has defined as outside warranty coverage. If a heat exchanger fails and a technician finds scale buildup, the manufacturer has documented grounds to deny the claim.
Consistent descaling service is one of the strongest protections against that outcome. A service record showing annual or semi-annual maintenance visits demonstrates the unit wasn’t neglected, which matters across manufacturers regardless of brand. Scale buildup combined with a lack of maintenance is among the most common reasons warranty claims get rejected, so the maintenance log itself becomes part of your coverage.
Building the Right Descaling Schedule for Your Home
The standard manufacturer recommendation is once a year under normal water conditions. For most of Orange County, “normal” isn’t the right baseline. A home with water hardness above roughly 7 to 10.5 GPG should move to a six-month descaling schedule. At those levels, mineral deposits build faster than annual flushing can address, and waiting 12 months means the unit spends half the year running with meaningful scale already present.
There are two ways to approach this. The first is to flush more frequently, scheduling professional descaling every six months to stay ahead of buildup. The second is to treat the water at the source. A whole house water softener reduces hardness to near zero before water ever reaches the tankless unit, which can bring a high-hardness home back into the range where annual maintenance is sufficient. For homeowners in cities like Anaheim or Lake Forest, where water hardness regularly exceeds the warranty threshold, a softener isn’t just a convenience upgrade. It’s a cost-benefit decision worth running the numbers on.
Some units also benefit from an inlet water filter, which catches sediment before it enters the heater. This is separate from a softener and doesn’t address hardness, but it reduces particulate wear on internal components and is worth including in any full maintenance conversation.
What a Professional Descaling Visit Actually Involves
Before any descaling can happen, the unit needs isolation valves on the hot and cold inlet lines. These valves allow the heater to be disconnected from the home’s water supply so a submersible pump can be connected and descaling solution can be circulated through the system. Many older installations in Orange County don’t have these valves in place. If yours doesn’t, adding them is the first step. It affects both the cost and the scope of that first service visit. A home that does have them installed can be serviced more quickly and for less labor on every future visit.
Once the unit is isolated, the process involves connecting hoses from the submersible pump through the cold inlet and out the hot outlet, creating a closed loop. A descaling solution (typically food-grade white vinegar or a manufacturer-approved citric acid solution) is circulated through the heat exchanger and internal components for 45 to 60 minutes. This dissolves mineral deposits without damaging metal surfaces. Manufacturers explicitly advise against harsh chemical cleaners like CLR; food-grade vinegar or an approved descaling product is the right call. After the flush, a technician inspects the inlet filter screen, checks for error codes, and verifies flow rates are back to normal. On a condensing tankless water heater, which uses a secondary heat exchanger to capture additional heat from exhaust gases, there are two heat exchangers to service rather than one, which adds time and complexity to the visit.
Our licensed plumbing technicians service all tankless water heater makes and models (not only Lennox equipment) and we’re available for same-day and 24/7 emergency scheduling when a scale-related issue leaves your home without hot water.
Warning Signs Scale Is Already a Problem
Scale buildup rarely announces itself all at once. It accumulates gradually, and the early signs are easy to dismiss as something else. These are the most consistent indicators we see that scale has progressed to the point of affecting performance:
- Reduced hot water flow: Water from faucets or showerheads is noticeably weaker, cuts in and out, or shuts off unexpectedly. This often means scale is restricting flow through internal components or the inlet filter screen is clogged with mineral debris.
- Error codes for restricted flow or blocked exhaust: Modern tankless units log faults. Codes pointing to flow restriction or blocked venting with no obvious external cause frequently trace back to scale accumulation rather than a mechanical failure.
- Unexpected shutoffs: The unit triggers automatic shutoffs to protect itself from overheating when heat can’t transfer efficiently through a scaled heat exchanger. The unit isn’t broken. It’s doing exactly what it’s designed to do when scale has reduced its ability to manage temperature.
- Knocking, banging, or popping sounds: These come from water boiling against scale-coated surfaces inside the heat exchanger. It’s the same process that makes a kettle noisy when it’s heavily scaled.
- Fluctuating water temperature: Hot water that surges or drops without you adjusting the tap can mean scale is interfering with the flow sensors and temperature controls the unit relies on to modulate output.
Any one of these symptoms in a home with hard water is a reasonable prompt to schedule a descaling visit before the problem compounds.
Protecting Performance & Warranty Coverage Long-Term
A single annual flush recommendation doesn’t hold up where tap water regularly runs between 15 and 19 GPG. Matching your descaling schedule to your home’s actual water hardness protects both day-to-day performance and the warranty coverage you paid for when the unit was installed. For many Orange County homes, that means either a six-month service schedule or an honest look at whether a whole-home water softener changes the economics in your favor.
If you’re not sure what your water hardness is or what maintenance your current setup actually needs, Comfort Air offers free in-person estimates. We’ll assess your system, check whether isolation valves are in place, and walk you through your options, including financing for descaling service or a softener installation if that’s the right direction. Give us a call at (760) 276-5144 to get started.