Tankless Water Heater Error Codes Explained: What They Mean and What to Do Next

Modern tankless water heaters are equipped with advanced diagnostic systems designed to identify problems before they become major issues. When something isn't operating correctly, the unit displays an error code that helps pinpoint the source of the problem.

Understanding what these error codes mean can help homeowners take appropriate action, determine whether a simple reset may solve the issue, or know when it's time to contact a qualified service professional.

In this guide, we'll explain some of the most common tankless water heater error code categories, potential causes, and recommended troubleshooting steps.

Why Do Tankless Water Heaters Display Error Codes?

Unlike traditional storage tank water heaters, tankless systems continuously monitor critical components such as:

• Ignition systems
• Gas supply
• Water flow rates
• Venting performance
• Heat exchanger temperatures
• Flame detection systems

When the system detects an abnormal condition, it displays an error code to help identify the issue.

These diagnostic features improve safety, reduce downtime, and make troubleshooting more efficient.

Common Causes of Tankless Water Heater Error Codes

Many error codes fall into a few common categories:

Ignition Problems - The unit cannot successfully ignite the burner.

Possible causes include:

• Interrupted gas supply
• Dirty ignition components
• Low gas pressure
• Faulty flame sensors
  
  

Venting Issues - Proper airflow is essential for safe operation.

Possible causes include:

• Blocked vent pipes
• Obstructions at vent terminations
• Improper vent installation
• Restricted combustion airflow
  
  

Water Flow Problems - Tankless water heaters require adequate water flow to activate.

Possible causes include:

• Clogged inlet filters
• Scale buildup
• Closed service valves
• Plumbing restrictions
  
  

Overheating Conditions - The system may shut down to prevent damage.

Possible causes include:

• Scale accumulation inside the heat exchanger
• Restricted water flow
• Failed temperature sensors
• Excessive operating temperatures
  
  

For a complete overview of common system issues, see our guide on How to Troubleshoot a Tankless Water Heater.

Common Noritz Error Codes and What They Mean

Error Code 11 – Ignition Failure

One of the most frequently encountered error codes, Error Code 11 indicates the burner failed to ignite.

Possible Causes:

• Gas supply interruption
• Closed gas valve
• Ignition system malfunction
• Venting obstruction

Recommended Actions:

• Verify gas service is active.
• Confirm the gas valve is open.
• Reset the unit.
• Inspect venting for obstructions.

If the error returns, professional diagnosis may be required.

Error Code 16 – Overheat Warning

Error Code 16 indicates the unit has detected excessive temperatures.

Possible Causes:

• Scale buildup in the heat exchanger
• Restricted water flow
• Sensor malfunction
• Maintenance overdue

Recommended Actions:

• Check water filters.
• Schedule descaling service.
• Verify adequate water flow through the system.

Regular maintenance is one of the best ways to prevent overheating-related shutdowns.

Error Code 90 – Combustion Abnormality

Error Code 90 generally relates to combustion performance.

Possible Causes:

• Airflow restrictions
• Venting problems
• Gas supply issues
• Dirty combustion components

Recommended Actions:

• Inspect vent terminations.
• Ensure adequate airflow around the unit.
• Verify gas pressure.
• Schedule professional service if necessary.
  
  

Can a Simple Reset Fix the Problem?

In some cases, yes.

Temporary issues such as power interruptions or minor operating irregularities may be resolved by resetting the unit.

Before Resetting:

• Record the error code.
• Consult the owner's manual.
• Verify gas, power, and water supplies.

If the Error Returns:

Repeated error codes usually indicate an underlying issue that requires further diagnosis.

Visit the Noritz Support Center for manuals, troubleshooting resources, and technical assistance.

How to Prevent Error Codes

While not every issue can be avoided, proper maintenance significantly reduces the likelihood of system faults.

Best Practices:

• Flush and descale annually.
• Clean inlet water filters regularly.
• Inspect venting systems periodically.
• Schedule professional maintenance.
• Address minor issues before they become major repairs.

Preventive maintenance helps improve efficiency, extend equipment lifespan, and reduce unexpected service interruptions.

When to Contact a Professional

Some error codes can indicate safety-related concerns that should only be addressed by qualified technicians.

Contact a professional if:

• Error codes persist after resetting.
• Gas supply issues are suspected.
• Venting problems are identified.
• Water leaks are present.
• The system repeatedly shuts down.

Use the Noritz Contractor Finder to locate a certified service professional near you.

Is It Time to Upgrade?

If your water heater frequently displays error codes, requires repeated repairs, or is nearing the end of its service life, replacement may be a more cost-effective long-term solution.

The Noritz EZ Series PRO features advanced diagnostics, simplified installation, enhanced efficiency, and long-term reliability designed to help minimize downtime and improve homeowner confidence.

Frequently Asked Questions