Tankless Water Heater Maintenance: A Complete Guide

Why Tankless Maintenance Matters More in the Permian Basin

A tankless water heater is a precision appliance. Unlike a tank heater that simply stores and heats water in a large vessel, a tankless unit forces water through a compact heat exchanger with narrow passages, heating it on demand as it flows. Those narrow passages are exactly what makes tankless units efficient—and exactly what makes them vulnerable to mineral scale buildup in hard water conditions.

In the Permian Basin, municipal water hardness ranges from 15 to 25 grains per gallon (gpg). The national average is about 7 gpg. At 20+ gpg, dissolved calcium and magnesium precipitate out of the water rapidly as it is heated, depositing scale on the heat exchanger surfaces. According to the Water Quality Association, scale buildup of just 1/16 of an inch on a heat exchanger can reduce efficiency by 11%. At 1/8 of an inch—which can accumulate in as little as 12–18 months without descaling in Permian Basin water—efficiency drops by over 25%, and the unit begins working harder, running hotter, and consuming more gas to deliver the same water temperature.

Every major tankless manufacturer—Rinnai, Navien, Noritz, Rheem, and others—specifies annual descaling as a maintenance requirement. In hard water areas, most manufacturers recommend descaling every 6–12 months. Failure to descale voids the warranty on many units. Rinnai's warranty terms, for example, explicitly require annual maintenance including descaling in areas with water hardness above 11 gpg. At 15–25 gpg, there is no ambiguity: annual descaling is mandatory to maintain your warranty and your unit's performance.

At Resolv Services (TX License #42668), we install and maintain all major brands of tankless water heaters across Odessa, Midland, Andrews, Monahans, Pecos, and the broader Permian Basin. We recommend annual professional descaling for every tankless unit in our service area—no exceptions. Call (432) 290-8511 to schedule your annual service.

Annual Descaling: The Essential Service

Descaling (also called flushing or deliming) is the process of circulating an acidic solution through the heat exchanger to dissolve mineral deposits. It is the single most important maintenance task for any tankless water heater, and in Permian Basin hard water, it is non-negotiable.

The professional descaling process takes approximately 60–90 minutes. Your plumber shuts off the gas supply to the unit and closes the hot and cold isolation valves (these are the dedicated shutoff valves on the water lines immediately before and after the tankless unit). The plumber connects a small submersible pump and two hoses to the service ports on the isolation valves, creating a closed circulation loop. A 5-gallon bucket is filled with food-grade white vinegar or a commercial descaling solution (such as Flow-Aide or Hercules Haymaker). The pump circulates the solution through the heat exchanger for 45–60 minutes, dissolving the accumulated calcium and magnesium deposits. After flushing, the plumber opens the isolation valves, restores gas, and verifies proper operation including ignition, flame pattern, and temperature output.

The DIY version uses the same basic process. A tankless flush kit (available at plumbing supply houses and online for $75–$125) includes a small submersible pump, two connection hoses, and a bucket. You supply the descaling solution—four gallons of food-grade white vinegar ($3–4 per gallon) works well for moderate scale. For heavy buildup, a commercial descaler is more effective. The complete DIY procedure takes about 90 minutes and costs $30–50 in supplies after the initial kit purchase.

Whether you do it yourself or hire a professional, the important thing is that descaling happens annually—or every 6 months if your water hardness is above 20 gpg and you do not have a water softener. A professional service costs $150–$250 and includes a full system inspection beyond just the descaling. Call (432) 290-8511 to schedule your annual tankless maintenance with Resolv Services.

Complete Maintenance Checklist: Beyond Descaling

While descaling is the headline task, a thorough annual tankless maintenance service includes several additional checks and cleaning steps that keep the unit running safely and efficiently.

Air filter cleaning is essential on indoor tankless units. The air filter (also called the air intake screen) prevents dust and debris from entering the combustion chamber. In West Texas, where dust is a constant presence—especially during spring sandstorms—the air filter can clog faster than in other climates. A clogged air filter restricts combustion airflow, causing the unit to run less efficiently and potentially triggering error codes. The filter is located on the front or bottom of the unit and typically slides out for cleaning. Rinse it under running water, let it dry completely, and reinstall it. Check it every 3–6 months in Odessa.

Inlet filter screen cleaning catches sediment before it enters the heat exchanger. The cold water inlet to the tankless unit has a small mesh screen that traps sand, grit, and large mineral particles. In Permian Basin water, this screen can accumulate debris quickly. Remove it by closing the cold water isolation valve, unscrewing the inlet fitting, and pulling out the screen with needle-nose pliers. Rinse it clean, inspect it for damage, and reinstall. A clogged inlet screen reduces water flow and can cause the unit to short-cycle or display a low-flow error.

Gas line and venting inspection ensures safe operation. A professional maintenance visit includes checking the gas line connections for leaks using an electronic gas leak detector or soap solution, inspecting the venting for proper pitch, secure connections, and any signs of corrosion or separation, and verifying that combustion air supply is adequate. For direct-vent and power-vent units, the exhaust termination point on the exterior wall should be checked for obstructions such as bird nests, spider webs, or landscaping that has grown too close.

Error code history review is part of every professional service visit. Most modern tankless units store a history of error codes and operational anomalies. Your plumber can access this history through the unit's diagnostic mode and identify any patterns—such as frequent ignition failures, flame rod issues, or temperature sensor anomalies—that indicate developing problems before they cause a complete failure.

Brand-Specific Maintenance Notes: Rinnai, Navien, and Noritz

While the core maintenance procedures are similar across brands, each manufacturer has specific requirements and features that affect how maintenance is performed. Here are the key differences for the three brands we install most often at Resolv Services.

Rinnai (RU and RE series) is the brand we install most frequently for tankless applications in Odessa and Midland. Rinnai units have a dedicated descaling mode that you activate through the controller by pressing a specific button sequence. When descaling mode is active, the unit opens internal valves to allow circulation through the heat exchanger without firing the burner. Rinnai requires annual maintenance by a licensed professional for warranty compliance in hard water areas (above 11 gpg). The RU series has a scale detection feature that monitors heat exchanger efficiency and alerts you (via error code LC) when descaling is needed. This is particularly useful in the Permian Basin because it provides a real-world indicator based on your actual water conditions rather than a fixed calendar schedule.

Navien (NPE and NCB series) units feature a built-in recirculation pump on many models, which is an additional component that requires maintenance. The recirculation pump should be checked annually for proper operation and any signs of mineral buildup on the impeller. Navien's ComfortFlow system uses a small buffer tank (0.5 gallon) that should be drained and inspected during annual service. Navien units are also known for their dual stainless steel heat exchangers, which are more resistant to scale than single copper heat exchangers but still require regular descaling in Permian Basin conditions. Navien's warranty requires that the unit be maintained according to their maintenance schedule, which includes annual descaling.

Noritz (EZ and NRCP series) units use a copper alloy heat exchanger that is efficient but more susceptible to scale buildup than stainless steel. In Permian Basin water, we recommend descaling Noritz units every 6 months rather than annually. Noritz units have a diagnostic display that shows operating parameters including inlet and outlet temperature, flow rate, and error history. The EZ series has a simplified maintenance access panel that makes descaling connections easier. Noritz requires annual maintenance for warranty compliance and recommends that a water softener be installed when water hardness exceeds 11 gpg—a threshold that every home in Odessa exceeds.

Common Error Codes and What They Mean

Tankless water heaters communicate problems through error codes displayed on the unit's controller or remote. Knowing what the most common codes mean can help you determine whether you can resolve the issue yourself or need to call a plumber.

Error Code 11 (Rinnai) or 011 (Navien): No ignition. The unit attempted to fire but did not detect a flame. Common causes include a gas supply interruption (check that the gas valve is open), a dirty or failed flame rod (a thin metal probe in the combustion chamber that detects flame), or a blocked exhaust vent. If gas is flowing and the vent is clear, the flame rod likely needs cleaning or replacement. This is a professional repair ($100–$200).

Error Code 12 (Rinnai) / 012 (Navien) / 12 (Noritz): Flame failure. The unit ignited but the flame went out during operation. This can indicate a dirty flame rod, inadequate gas pressure, combustion air restriction, or wind interference on an outdoor unit. If the unit restarts normally after resetting, monitor it. If it repeats, call a plumber to diagnose the underlying cause.

Error Code LC (Rinnai) or 003 (Navien): Scale buildup detected or maintenance required. This code means the unit has detected reduced heat exchanger efficiency consistent with scale buildup. It is a descaling reminder, not an emergency. However, continuing to operate the unit without descaling will worsen efficiency and may eventually cause overheating shutdowns. Schedule a descaling service promptly. This is the most common code we see on Rinnai units in Odessa.

Error Code 16 (Rinnai / Noritz): Overheating. The heat exchanger temperature exceeded safe limits, and the unit shut down to prevent damage. This is often caused by heavy scale buildup restricting water flow through the heat exchanger (which means the unit is long overdue for descaling), a failing flow sensor, or a blocked water filter. Do not ignore this code—repeated overheating can damage the heat exchanger. Call (432) 290-8511 for same-day service on overheating errors.

DIY vs. Professional Maintenance: Making the Right Choice

Some tankless maintenance tasks are straightforward DIY projects, while others require professional tools, training, and a licensed plumber. Knowing the distinction helps you save money on the tasks you can handle while ensuring the critical tasks are done right.

DIY-friendly tasks include air filter cleaning (remove, rinse, dry, reinstall—10 minutes), inlet filter screen cleaning (close valve, remove screen, rinse, reinstall—15 minutes), and descaling if you own a flush kit and are comfortable connecting and disconnecting service port hoses. The total cost for DIY annual maintenance is $30–50 for vinegar and replacement screens, plus the one-time $75–$125 cost for a flush kit.

Tasks that require a professional include gas leak testing (requires an electronic gas leak detector or combustion analyzer), venting inspection (requires knowledge of manufacturer-specific venting codes and clearances), flame rod cleaning or replacement (requires opening the combustion chamber), error code diagnosis beyond basic codes (requires manufacturer training and diagnostic tools), and gas valve or flow sensor replacement (requires licensed gas work). Professional annual maintenance costs $150–$250 and covers all tasks—both DIY-level and professional-level—in a single visit.

Our recommendation for Permian Basin homeowners: have a professional service performed annually and supplement with DIY air filter cleaning every 3–6 months between professional visits. The professional service ensures warranty compliance, catches developing problems early, and includes the gas safety checks that only a licensed plumber should perform. Resolv Services (TX License #42668) provides comprehensive annual tankless maintenance for all major brands. We document every service visit and provide a written report that you can retain for warranty records. Call (432) 290-8511 to schedule your annual service or to sign up for our maintenance program that includes priority scheduling and a discount on the annual service fee.