Tankless water heaters are one of the smartest investments Atlanta homeowners can make for endless hot water and energy savings. But like any appliance, they sometimes display error codes when something isn’t working right.

If you’ve seen a code flash on your Rinnai, Noritz, Navien, or other tankless units, it’s your water heater’s way of telling you there’s a problem. Some issues are simple to resolve—but many require a licensed professional to safely diagnose and repair.

At Sundial Plumbing, we help homeowners across Atlanta, Kennesaw, Marietta, and beyond every week with tankless water heater troubleshooting, repairs, and replacements. Here’s what you need to know about common error codes, what you can try yourself, and when to call us.

Common Tankless Water Heater Error Codes

Different brands use different codes, but the issues are often similar.

🔥 Ignition / Flame Failure

  • Rinnai: Code 11 (ignition), Code 12 (flame failure)

  • Noritz: Code 11 (ignition), Code 12 (flame failure)

  • Navien: Error E003 (ignition failure), Error E012 (flame loss)

Meaning: The unit can’t ignite or keep the flame burning.
Possible causes: Gas supply interruption, dirty flame sensor, or venting issue.
Homeowner check: Make sure your gas is turned on and breakers aren’t tripped.
When to call Sundial: If it persists, our techs test burners, sensors, and gas pressure.

💧 Flow Sensor / Water Supply Issues

  • Rinnai: Code 10 (air supply/flow), Code 65 (water flow sensor)

  • Noritz: Code 29 (flow abnormality), Code 45 (water leakage detection)

  • Navien: Error E027 (flow sensor issue), Error E110 (abnormal water pressure)

Meaning: The system detects irregular water flow.
Possible causes: Clogged inlet filter, closed valves, frozen or kinked pipes.
Homeowner check: Ensure valves are fully open and inspect for frozen lines.

⚠️ Overheating / Scale Buildup

  • Rinnai: Code 14 (thermal fuse), Code 16 (over-temperature)

  • Noritz: Code 16 (overheated heat exchanger)

  • Navien: Error E016 (overheating), Error E030 (heat exchanger scale buildup)

Meaning: Water temperature is too high or flow is restricted.
Possible causes: Mineral buildup (common in Atlanta’s hard water), blocked heat exchanger.
Homeowner check: If you’ve flushed before, you can try it. Otherwise, leave it to a pro.
Pro tip: Ask about HALO water treatment to prevent scale and extend tankless lifespan.

🌬️ Ventilation / Exhaust Blockage

  • Rinnai: Code 90 (improper combustion), Code 91 (flame rod circuit)

  • Noritz: Code 90 (combustion abnormality), Code 92 (fan abnormality)

  • Navien: Error E030 (blocked exhaust/vent), Error E046 (vent fan failure)

Meaning: Improper venting or restricted exhaust airflow.
Possible causes: Bird nest, debris, or installation problem.
Homeowner check: Check the exterior vent termination for blockages.

Free Estimates vs. Diagnostic Fees

Here’s an important distinction:

  • Free assessments: Perfect for new water heater installs, repipes, or planned upgrades.

  • Diagnostic service calls: Necessary when your tankless is showing error codes. A trained technician must open the unit, test components, and safely identify the root cause.

At Sundial Plumbing, we charge a fair, transparent diagnostic fee that covers our technician’s time and expertise. If repair or replacement is needed, you’ll get upfront pricing before any work begins.

Repair vs. Replacement: How to Decide

  • Repair makes sense if: The unit is under 10 years old, and parts are readily available.

  • Replacement is smarter if: The unit is older, has multiple failures, or repair costs are close to replacement.

👉 Ask about our specials:

  • $75 OFF standard plumbing repairs

  • $100 OFF tank water heater installs

  • $200 OFF tankless water heater installs

Why Choose Sundial for Tankless Repairs in Atlanta?

  • Local expertise: Serving Georgia since 1945.

  • Certified technicians: Experienced with Rinnai, Noritz, Navien, and more.

  • Upfront pricing: No surprises, no hidden fees.

  • Water quality solutions: HALO whole-home filtration to protect your investment.

📞 Call Sundial Plumbing today at (770) 427-1998 for fast, reliable service.

FAQs About Tankless Water Heater Error Codes

Q: Can I just reset my unit to clear the error?
A: Resetting may temporarily clear the code, but if the problem remains, it will come back. It’s important to find the root cause.

Q: How often should I flush my tankless water heater?
A: At least once a year in Metro Atlanta—more often if you don’t have a water treatment system.

Q: Do tankless heaters last longer than tanks?
A: Yes. With proper maintenance, tankless units last 15–20 years compared to 8–12 years for tanks.

Q: Will error codes mean I need a new heater?
A: Not always. Many are repairable with part replacements or cleanings. A Sundial technician can guide you on the best option.