Navien Tankless Water Heater Error Code 040: How to Fix It

Easy 15-30 minutes High Severity Verified June 2026
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Error Code
040
Brand
Navien
Product Type
water_heater
Severity
High
DIY Difficulty
Easy
Estimated Fix Time
15-30 minutes
Navien error code 040 indicates an air pressure fault caused by a blocked vent or flue. This typically means the exhaust or intake vent is obstructed, preventing the heater from operating safely. Before troubleshooting, turn off the unit and allow it to cool.
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Tools You'll Need

How to Fix Error Code 040

  1. Turn Off Power and Gas

    Always turn off gas and electricity before servicing to prevent injury or fire.

  2. Inspect Vent Pipes for Blockages

  3. Clear Any Debris

    Do not use sharp tools that could damage the vent pipe.

  4. Check for Kinks or Damage

  5. Reset the Water Heater

    If error persists after clearing vents, contact a professional.

Parts You May Need

Vent pipe section
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Vent termination cap
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Vent pipe section
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Vent termination cap
Check Price on Amazon
Vent pipe section
Check Price on Amazon
Vent termination cap
Check Price on Amazon
Vent pipe section
Check Price on Amazon
Vent termination cap
Check Price on Amazon
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When to Call a Professional

If the error returns after clearing all vents, or if you notice a damaged vent pipe, internal fan failure, or pressure switch problem, call a qualified Navien technician. Do not attempt to replace the fan or pressure switch yourself.

Frequently Asked Questions

What does Navien error 040 mean?
Error 040 indicates an air pressure fault, usually caused by a blocked or restricted vent (exhaust or intake) on your tankless water heater.
Can I reset Navien error 040?
Yes, after clearing any blockages, you can reset the unit by pressing the Reset button or turning the power off and on. If the error persists, the issue may be internal.
How do I prevent Navien error 040?
Regularly inspect vent terminals for debris, snow, or nests. Keep the area around the water heater clear. Annual professional maintenance can help prevent vent blockages.
Is error 040 dangerous?
Yes, because it indicates improper exhaust venting, which can lead to carbon monoxide buildup. Do not operate the heater until the blockage is cleared.

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