Why does my Boerne tankless water heater keep shutting off?

The most common cause across the Boerne service market is scale buildup on the heat exchanger triggering the Navien E016 or Rinnai Code 16 over-temperature shutdown. The 358 mg/L hard water concentration deposits calcium and magnesium carbonate scale on the inside of the heat exchanger coil at a rate roughly 2 to 3 times faster than national-average water. As the scale accumulates, it acts as an insulating layer between the burner flame and the water, which forces the burner to run hotter to push heat through the insulation. The unit detects the overheating condition and shuts down to protect itself from cracking the heat exchanger. Other common causes include the Navien LC or Rinnai LC service reminder running past due for descaling, scale and carbon buildup on the flame rod sensor causing E012 or Code 12 flame loss errors, and clogged inlet filters on well water properties causing flow sensor errors. Most of these issues resolve with a $200 to $450 professional descaling and flush service when caught before heat exchanger damage occurs.

How often should a Boerne tankless water heater be flushed?

The manufacturer-recommended 12-month descaling interval is unrealistic for the Boerne market. The 358 mg/L hard water concentration produces scale accumulation rates that justify a 6-to-9-month professional descaling interval for any tankless unit operating without a water softener. Most Boerne Navien LC and Rinnai LC service reminder codes appear at the 6 to 9 month mark rather than the manufacturer-anticipated 10 to 12 months. Properties with properly sized whole-house softeners (32,000 to 64,000 grain capacity depending on household size) can typically extend the descaling interval to 12 months because the softened water no longer carries the dissolved calcium and magnesium ions that create scale. Properties on private wells in Bergheim, Welfare, Sisterdale, and rural Kendall County often need additional sediment pre-filtration and may need flushing every 6 months even with a softener installed. Annual maintenance contracts in the Boerne market typically run $250 to $500 and include the scheduled flush plus discounted service rates on any repairs that come up during the year.

Should Boerne homeowners repair or replace an aging tankless water heater?

The decision depends on the age of the unit, the cost of the proposed repair, and whether a water softener is part of the long-term plan. Tankless units in the Boerne 358 mg/L water environment without a softener typically reach end-of-service-life in the 8 to 12 year range rather than the 15 to 20 year range that manufacturer marketing promises. A $2,500 heat exchanger replacement on a 9-year-old Navien with no softener installation often makes less economic sense than a $6,500 condensing tankless replacement that includes proper softener integration and resets the manufacturer warranty clock. A $300 descaling and flame rod cleaning visit on a 4-year-old Rinnai with a softener already installed makes complete sense and protects the existing warranty. The diagnostic conversation should always include the water treatment status because the same repair quote on the same unit can produce very different outcomes depending on whether the underlying water chemistry gets addressed.

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Last updated:2026 Apr, Thu

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