The pitch that sold you on a tankless water heater probably included something like “no tank means no maintenance.” It’s an understandable leap. Without a forty-gallon reservoir slowly accumulating sediment, it seems like there’s nothing to manage. But the actual mechanism inside these units tells a different story, and it’s one worth understanding before you skip another service appointment.
Every time your tankless unit fires, cold water passes directly through a heat exchanger to be heated on demand. That exchanger contacts fresh, mineral-bearing water thousands of times a year. No storage tank doesn’t mean no mineral exposure. It means continuous mineral exposure, without the buffer a tank provides. We’ve been servicing water heaters in Cleburne since 1997, and the pattern we see in neglected tankless units is consistent: the damage isn’t dramatic until it suddenly is.
Why Tankless Systems Still Need Attention
The heat exchanger is where all the work happens. Cold water enters, travels through a coiled or channeled metal path, gets blasted with heat from a gas burner or electric element, and exits hot. It’s efficient precisely because the contact surface is compact and the transfer happens fast.
That compact design is also what makes scale a real problem. Calcium and magnesium dissolved in tap water don’t stay dissolved when they hit high heat. They precipitate out and adhere to the interior surfaces of the exchanger. Each heating cycle leaves a microscopic residue. Over months and years, those deposits build into a visible crust that acts as an insulating layer, forcing the burner to work harder and run longer to reach the set temperature. The unit’s Uniform Energy Factor drops as scale accumulates, and the heat exchanger itself takes on stress it wasn’t designed to handle indefinitely.
Why Cleburne’s Water Makes This More Urgent
Cleburne’s water supply draws from two surface sources (Lake Pat Cleburne and Lake Aquilla) along with groundwater wells tapping the Twin Mountain-Travis Peak formation of the Trinity Aquifer. The Texas Water Development Board classifies groundwater in the Trinity Aquifer’s outcrop areas as fresh but very hard. Hard water, generally defined as carrying more than 120 milligrams per liter as calcium carbonate, accelerates scale formation significantly compared to soft-water regions. The standard once-a-year flush schedule assumes moderate hardness. Homes drawing from Cleburne’s supply can reach the same level of internal scale buildup in six to eight months that a soft-water home accumulates over a full year.
That’s not a reason to panic. It’s a reason to be honest about your service interval rather than defaulting to the generic calendar in most installation manuals. A water softener can also address the problem at the source by reducing the mineral load before water ever reaches the heat exchanger, something we can evaluate during a service visit.
What Skipping Maintenance Actually Costs
Most homeowners who skip tankless maintenance don’t think of it as a decision. They just don’t schedule anything, and nothing obviously breaks for a year or two. The costs accumulate quietly before the expensive failure shows up.
Utility Bills
A scale-insulated heat exchanger draws more energy to heat the same volume of water. The increase is gradual enough that it rarely registers as an obvious spike, but studies on scale buildup in residential water heaters consistently show efficiency losses of 8 to 12 percent with moderate accumulation.
Warranty Coverage
Rinnai’s warranty documentation requires annual flushing of the heat exchanger to remove scale, and claims tied to water quality damage can be denied when maintenance records don’t support compliance. Navien’s owner’s manual states that failure to perform maintenance as outlined may void the limited warranty. Heat exchanger replacements can run $500 to $1,500 in parts alone, not counting labor. When that failure is traced to mineral buildup and there’s no service record, the warranty that looked like a safety net doesn’t apply.
What a Professional Maintenance Visit Covers
A full tankless maintenance visit isn’t a vague “check of the unit.” The core task is descaling: a vinegar-based or manufacturer-approved solution is circulated through the heat exchanger for roughly 45 to 90 minutes to dissolve mineral deposits, followed by a clean water flush. Beyond that, several other components get attention.
- Inlet water filter: This screen catches sediment before it reaches the heat exchanger. A partially clogged filter reduces water flow, which trips flow sensors and causes inconsistent heating. It gets removed, cleaned, and reinstalled.
- Combustion venting and air intake: Gas units draw air for combustion and exhaust through dedicated vents. Blocked or improperly sealed venting affects both burner efficiency and safety. We inspect both during every gas unit service.
- Pressure relief valve: This safety device prevents dangerous pressure buildup. Testing it takes a few minutes and confirms it’s still functioning correctly.
- Error code history: Most modern units log fault codes internally. Pulling that history before clearing it tells us whether the unit has been flagging issues between service visits.
Signs You Shouldn’t Wait On
Annual maintenance is the goal, but some units give clear signals that service is needed before the calendar says so. Catching them early keeps a minor issue from becoming a heat exchanger replacement.
LC or Scale-Related Error Codes
Rinnai units display an LC code when the unit detects lime or scale buildup affecting performance. Navien units have their own scale-related diagnostic codes. Don’t clear the code and move on. Schedule a flush.
Temperature Swings Mid-Shower
Water that alternates between hot and lukewarm during a single shower often points to a flow sensor struggling to read accurately through scale buildup, or a heat exchanger that can’t maintain consistent transfer.
Reduced Hot Water Pressure
If hot water pressure has dropped while cold water flow seems normal, the restriction is likely inside the unit. Scale can narrow the passages inside the heat exchanger, or sediment can be partially blocking the inlet filter. Both are addressed during a standard maintenance visit.
A Small Habit That Protects a Big Investment
A tankless water heater costs more upfront than a tank unit, and the efficiency and longevity that justify that cost depend on keeping the heat exchanger clean. A routine flush once a year, or more frequently given Cleburne’s water hardness, is what preserves both performance and manufacturer warranty coverage.
Our master plumber-led team at Curly's Plumbing Inc. can build that maintenance check into any water heater visit. For homes dealing with hard water at the source, we also offer water softener evaluation and on-site water testing. Give us a call at (817) 859-6762 to set something up.