Navien Tankless Water Heater Error Code 004: How to Fix It

Medium 30-60 minutes Medium Severity Verified June 2026
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Error Code
004
Brand
Navien
Product Type
water_heater
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
30-60 minutes
Error code 004 on your Navien tankless water heater indicates a flame sensor short circuit. This means the flame sensor is malfunctioning or there is an electrical issue in the sensor circuit. It can cause the heater to shut down unexpectedly. Follow these steps to troubleshoot and fix the problem.
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Tools You'll Need

How to Fix Error Code 004

  1. Power Off and Isolate the Unit

    Risk of electric shock. Always disconnect power before servicing.

  2. Locate the Flame Sensor

    Components may be hot. Allow the unit to cool completely.

  3. Inspect the Flame Sensor and Wiring

  4. Clean or Replace the Flame Sensor

    Use only genuine Navien replacement parts to ensure proper operation.

  5. Check the Control Board (if sensor is fine)

    Control board replacement should only be done by a qualified technician if you are not experienced with electronics.

  6. Reassemble and Test

    Watch for gas leaks. Use a soapy water solution on gas connections to verify no leaks.

Parts You May Need

Flame Sensor
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Flame Sensor
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Flame Sensor
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Flame Sensor
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When to Call a Professional

If the flame sensor and wiring check out fine but the error persists, the control board may need replacement. Professional help is also recommended if you are uncomfortable working with electrical components or gas connections.

Frequently Asked Questions

What does Navien error code 004 mean?
Error code 004 indicates a flame sensor short circuit. The water heater's control board detects an abnormal electrical path in the flame sensor circuit, causing the unit to shut down for safety.
Can I reset Navien error code 004?
You can try resetting the unit by turning off power and gas for 30 seconds, then turning them back on. However, if the underlying issue isn't fixed, the code will return.
How do I clean a Navien flame sensor?
Turn off power and gas, remove the front cover, locate the flame sensor rod, and gently clean it with fine-grit sandpaper or a scouring pad. Avoid using harsh chemicals.
Is it safe to use the water heater with error code 004?
No. The error indicates a safety issue. Operating the unit could lead to improper combustion or gas leaks. Turn off the water heater and troubleshoot immediately.
How much does it cost to fix Navien error code 004?
DIY replacement of the flame sensor costs around $30-$60 for the part. Professional service including control board replacement can range from $200-$500.

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