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Diagnostic Fault Codes

Tankless Water Heater Error Codes

Modern tankless water heaters monitor operation continuously, displaying numeric fault codes when sensors detect ignition, airflow, temperature, or flow anomalies.

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Tankless Water Heater Error Codes diagnostic overview
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Quick answer

What do tankless water heater error codes mean?

Tankless water heater error codes are diagnostic indicators generated by the unit's control board to identify specific operating faults such as ignition failure, flame loss, exhaust venting blockage, overheating thermistors, water flow sensor faults, or electrical communication errors.

Updated ยท Reviewed by the TanklessFixer technical team

Technical Overview

Understanding Tankless Diagnostic Codes

Microprocessor control boards monitor dozens of safety switches, temperature thermistors, flame rods, and pressure sensors during every firing cycle. When a sensor reading falls outside programmed safety tolerances, the unit halts operation and displays a numerical code on the digital controller.

Understanding error code categories helps determine whether an issue requires simple maintenance like filter cleaning, gas supply checks, or professional component replacement.

Symptoms & Warnings

Common Signs Your System Needs Attention

  • Digital remote controller or unit display flashing numeric codes (e.g., Code 11, Code 12, E1)
  • System abruptly shutting off during hot water use and requiring power resets
  • Beeping warning alerts sounding from the main control panel
  • Unit attempting ignition multiple times before lock-out mode is triggered
  • Red diagnostic LED indicators illuminated on internal circuit boards
  • Persistent code reappearing immediately after cycling electrical power
Core Factors

Common Error Code Categories

Ignition & Flame (Codes 11/12)

Failing to ignite or losing flame signal during combustion due to dirty flame rods or gas issues.

Airflow & Venting (Codes 10/90)

Blocked exhaust vents, clogged air intake screens, or failing combustion blower motors.

Overheating & Scale (Codes 14/E5)

Thermal high-limit switches tripping due to mineral scale buildup in heat exchangers.

Sensor & Thermistor (Codes 31-34)

Open or short-circuit faults in incoming or outgoing water thermistors.

Diagnostic Categories

Key Focus Areas

01

Ignition Lockout Codes

Indicate gas supply interruptions, dirty igniters, or oxidized flame rods preventing stable combustion.

02

Airflow & Exhaust Codes

Signal intake pipe obstructions, venting backpressure, or intake fan speed discrepancies.

03

Thermal Protection Codes

Trigger when heat exchanger temperatures exceed safe limits due to restricted water flow or heavy scale.

04

Water Flow Sensor Codes

Occur when flow turbine sensors fail to report expected rotation signals to the control module.

Service Process

How to Safely Handle Error Codes

  1. Record Displayed Code

    Note the exact numeric error code flashing on the digital wall controller or front panel.

  2. Check Basic Supplies

    Verify gas supply valves are fully open, cold water inlet is clear, and electrical power is stable.

  3. Perform Safe Reset

    Turn off remote controller power, wait 30 seconds, and turn back on to test if code clears.

  4. Professional Diagnosis

    If the code recurs, contact a qualified technician to inspect internal sensors, gas valves, or boards.

Brands

Brand Compatibility & Service

Tankless systems from major manufacturers can differ in components, diagnostics, maintenance procedures, and error-code definitions. Service resources cover major brands found in service areas across the country.

  • Condensing & non-condensing gas systems
  • Single-phase & 3-phase electric tankless
  • Whole-home & point-of-use equipment
  • RinnaiCondensing & non-condensing gas
  • NavienCondensing units & combi boilers
  • NoritzIndoor & outdoor gas models
  • RheemGas & electric tankless
  • TakagiResidential gas tankless
  • A. O. SmithCondensing gas tankless
  • BoschGas & electric tankless
  • Bradford WhiteInfiniti gas series
  • Stiebel EltronElectric tankless
  • EcoSmartElectric tankless
  • RichmondGas tankless
  • StateGas tankless
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FAQ

Frequently Asked Questions

Why does my tankless water heater keep showing the same error code?

Recurring codes indicate an uncorrected underlying hardware fault, such as a dirty flame sensor, scale-clogged heat exchanger, or failing circuit board.

Can clearing an error code fix the water heater?

Resetting power clears the code temporarily from memory, but if the mechanical or electrical fault remains, the code will reappear.

Do error codes differ by manufacturer?

Yes, while many manufacturers use similar numeric formats (like Code 11 for ignition failure on Rinnai or Noritz), definitions vary by brand.

What does Code 11 mean on a tankless water heater?

Code 11 typically indicates ignition failure, meaning the unit tried to light the gas burner but could not establish a flame.

What does Code 90 mean on a tankless water heater?

Code 90 usually indicates combustion airflow abnormality, caused by blocked air intake pipes, vent terminations, or fan speed issues.

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