Tankless water heater error code 11 usually indicates an ignition failure. This means the unit attempted to ignite the burner but was unable to establish a flame.

This issue can occur for several reasons, including gas supply problems, ignition component issues, or ventilation problems. Fortunately, many of these causes can be diagnosed with simple troubleshooting steps.

In this guide, we explain what error code 11 means and how to fix it.

Tankless Water Heater Error Code 11 Ignition Check Diagram

Tankless Heater Shows Error Code 11
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Check Gas Supply
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Check Gas Valve
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Check Igniter
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Check Flame Sensor
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Reset Heater
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Call Technician if Needed

What Does Tankless Water Heater Error Code 11 Mean?

Error code 11 is most commonly associated with ignition failure in gas-powered tankless water heaters.

This code appears when the system attempts to ignite the burner but cannot detect a stable flame.

Several manufacturers use this code, including:

• Rinnai
• Navien
• Rheem
• Noritz

Although the exact cause may vary slightly by brand, the troubleshooting process is similar.

Common Causes of Error Code 11

Several issues can prevent the heater from igniting properly.

The most common causes include:

• Gas supply interruption
• Closed gas valve
• Air in the gas line
• Venting or exhaust blockage
• Faulty ignition components
• Electrical connection issues

Understanding these potential causes helps determine the best solution.

Step-by-Step Troubleshooting for Error Code 11

If your tankless water heater displays error code 11, try the following troubleshooting steps before calling a technician.

Check the gas supply
Make sure the gas shut-off valve near the heater is fully open.
Inspect the vent pipe
Verify that the intake and exhaust vents are not blocked by debris, snow, or leaves.
Reset the system
Turn the unit off, wait about 30 seconds, and restart it.
Run hot water for several minutes
Sometimes air trapped in the gas line can temporarily prevent ignition.
Check electrical connections
Make sure the unit has power and that no breakers have tripped.

If the error code continues after these steps, additional inspection may be required.

1. Gas Supply Problems

A common reason for ignition failure is a lack of gas reaching the unit.

Possible causes include:

• Gas valve accidentally closed
• Gas line pressure issues
• Recently installed systems with air in the gas line

Check that the gas shutoff valve near the heater is fully open. If the system was recently installed or serviced, trapped air in the gas line may temporarily prevent ignition.

2. Venting or Exhaust Blockage

Tankless heaters require proper airflow to ignite safely.

Blocked vent pipes or restricted exhaust systems can prevent ignition and trigger error code 11.

Check for:

• debris in the vent pipe
• snow or leaves blocking outdoor vents
• damaged vent components

Clear airflow is essential for proper combustion.

3. Dirty Burner or Ignition Components

Over time, burners and ignition electrodes can accumulate dust or debris.

When this happens, the system may struggle to ignite the burner.

Routine tankless water heater maintenance helps prevent these problems by keeping internal components clean.

👉 See our guide on tankless water heater maintenance for recommended servicing practices.

4. Mineral Buildup Affecting Performance

Although scale buildup usually affects heating efficiency, severe mineral accumulation can also impact internal components.

Regular flushing helps prevent scale buildup inside the heat exchanger.

How to Reset a Tankless Water Heater After Error Code 11

In some cases, resetting the system may clear the error.

Typical reset steps include:

Turn off the unit using the power button.
Wait about 30 seconds.
Restore power to the system.
Run a hot water tap to restart the heater.

If the error code returns, further troubleshooting may be necessary.

Can Maintenance Help Prevent Error Code 11?

In some cases, poor maintenance can contribute to ignition problems.

For example, scale buildup inside the system can affect internal sensors or reduce heating efficiency.

Routine tankless water heater maintenance helps ensure components remain clean and functioning properly.

Regular flushing also removes mineral buildup that may affect performance.

👉 See our guide on how to flush a tankless water heater for step-by-step instructions.

When to Call a Professional

If basic troubleshooting does not resolve error code 11, a licensed technician may need to inspect the system.

Possible professional repairs include:

• replacing ignition electrodes
• repairing gas supply components
• diagnosing control board issues
• checking combustion settings

Professional servicing ensures the heater operates safely and efficiently.

Do Electric Tankless Water Heaters Show Error Code 11?

Most electric tankless water heaters use different diagnostic codes. Error code 11 is typically associated with gas-powered tankless systems that rely on ignition and combustion.

Because electric heaters do not use burners, ignition errors are generally not applicable to those models.

Related Tankless Water Heater Troubleshooting

Many common tankless water heater problems are related to maintenance or system demand.

👉For additional help diagnosing issues, see our complete tankless water heater troubleshooting guide.

Frequently Asked Questions

What brand uses error code 11 on tankless heaters?

Error code 11 is commonly used by brands such as Rinnai, Navien, Rheem, and Noritz to indicate ignition failure.

Can I fix error code 11 myself?

Some causes, such as checking gas valves or clearing vent blockages, can be handled by homeowners. However, internal component issues may require professional service.

Does maintenance help prevent error code 11?

Yes. Regular maintenance and flushing can help prevent ignition problems and improve system reliability.