This is a good next step because:
- goes with 11 / 12 / 29
- same intent
- easy to interlink
- keeps troubleshooting cluster strong
Tankless Water Heater Error Code 13 Combustion Check Diagram
Tankless Heater Shows Error Code 13
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Check Flame Sensor
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Check Gas Supply
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Check Air Intake
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Check Exhaust Vent
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Clean Inside Unit
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Reset Heater
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Call Technician
Tankless Water Heater Error Code 13 (Causes & Fixes)
Tankless water heater error code 13 usually indicates a problem with the combustion system or flame detection. When this error appears, the heater may shut down to prevent unsafe operation.
This type of error often happens when the unit cannot properly detect or maintain the burner flame.
In this guide, we explain what tankless water heater error code 13 means and how to troubleshoot the most common causes.
What Code 13 Means
Error code 13 indicates a flame failure during operation.
This means the unit is unable to maintain proper combustion after ignition, causing the system to shut down for safety.
In most cases, this is related to airflow issues, gas supply problems, or faulty ignition components.
Common Symptoms
When code 13 appears, you may notice:
- unit shuts down during operation
- no hot water or interrupted heating
- ignition starts but does not continue
- error code appears during use
- system stops to prevent unsafe combustion
These symptoms usually indicate a flame failure or combustion problem.
Dirty Flame Sensor
The flame sensor tells the heater that combustion is working correctly.
If the sensor becomes dirty or worn, the heater may think the flame has gone out even when it has not.
Symptoms may include:
• heater starts then shuts off
• repeated ignition attempts
• intermittent error codes
• no hot water
Routine tankless water heater maintenance helps keep sensors clean and working properly.
Flame detection problems like this are often related to tankless water heater error code 11, which occurs during initial ignition.
If the flame starts but cannot stay active, it may also trigger tankless water heater error code 12.
Gas Supply Problems
Tankless heaters require steady gas pressure to maintain the burner flame.
If gas flow is too low, the heater may not keep the flame running.
Possible causes include:
• closed gas valve
• low gas pressure
• air in gas line
• undersized gas pipe
Check that the gas shutoff valve is fully open.
If the problem continues, gas pressure may need to be tested.
If your unit is not producing hot water due to ignition or flame issues, see our guide on tankless water heater not heating.
Blocked Vent or Air Intake
Proper airflow is required for safe combustion.
If the vent or intake pipe is blocked, the flame may become unstable.
Check for:
• leaves or debris
• damaged vent pipes
• insects or nests
• improper installation
Airflow problems may cause the heater to shut down and show error code 13.
Loose Wiring or Sensor Problems
Tankless heaters use several sensors to monitor safe operation.
If wiring becomes loose, the heater may not detect the flame correctly.
Possible issues include:
• loose connections
• worn sensors
• damaged wiring
• control board faults
Electrical problems should be inspected carefully.
Control Board Problems
Tankless water heaters use an electronic control board to manage ignition, sensors, and safety systems.
If the control board malfunctions, the heater may not recognize the flame correctly and may display error code 13.
Possible signs include:
• random shutdowns
• repeated error codes
• heater works intermittently
• ignition starts but stops
Electrical components should be inspected by a qualified technician.
Improper Vent Installation
Incorrect vent installation can affect combustion and cause flame detection errors.
Possible problems include:
• vent pipe too long
• incorrect vent material
• poor airflow clearance
• intake and exhaust too close together
If the heater cannot maintain proper combustion, error code 13 may appear.
Installation problems should be corrected according to manufacturer instructions.
Overheating Protection
Tankless heaters include safety sensors that shut the system down if unsafe temperatures are detected.
Restricted airflow or heavy mineral buildup may cause overheating.
When overheating occurs, the heater may stop working and show error code 13.
Allow the unit to cool before restarting.
Mineral Buildup Affecting Performance
Heavy mineral buildup can affect internal sensors and heat transfer.
When scale forms inside the heater, the system may not operate correctly.
Flushing the heater helps remove mineral deposits.
See our guide on how to flush a tankless water heater for instructions.
Resetting the Heater
Sometimes the error only requires a reset.
Steps may include:
- Turn off the heater
- Wait about 30 seconds
- Restore power
- Run hot water again
If the error returns, further inspection may be needed.
Weak Flame or Gas Pressure Fluctuations
Tankless water heaters require a steady gas supply to keep the burner flame stable. If gas pressure fluctuates, the heater may lose the flame signal and display error code 13.
This can happen when:
• multiple gas appliances are running at the same time
• the gas regulator is not working correctly
• the gas line is too small for the heater
• the supply pressure is too low
When the flame becomes weak or unstable, the heater may shut down to prevent unsafe operation.
A technician can measure gas pressure and verify that the system is receiving the correct fuel supply.
When to Call a Professional
Call a technician if:
• error code keeps returning
• gas pressure problems are suspected
• sensors may be damaged
• venting problems exist
A licensed technician can safely diagnose the system.
Related Tankless Water Heater Troubleshooting
If your heater has other issues, see our complete tankless water heater troubleshooting guide for more help.
Frequently Asked Questions
What causes error code 13 on a tankless heater?
Error code 13 usually means the heater cannot detect the burner flame correctly.
Can a dirty sensor cause error code 13?
Yes. A dirty flame sensor is one of the most common causes.
Can maintenance prevent error code 13?
Yes. Cleaning and flushing the heater helps prevent sensor and combustion problems.
Conclusion
If your tankless water heater shows code 13, the issue is usually related to flame failure or combustion problems.
Start by checking for airflow restrictions, gas supply issues, or ignition component faults. These can prevent the unit from maintaining a stable flame.
If the problem continues, professional inspection may be required to ensure safe and proper operation.