Navien Water Heater Error Code 099: How to Fix It

Medium 30-60 minutes High Severity Verified June 2026
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Error Code
099
Brand
Navien
Product Type
water_heater
Severity
High
DIY Difficulty
Medium
Estimated Fix Time
30-60 minutes
Navien tankless water heater error code 099 indicates high flue gas pressure. This usually means a blockage in the exhaust vent or a problem with the combustion air supply. Ignoring this error can lead to safety hazards, so address it promptly.
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Tools You'll Need

How to Fix Error Code 099

  1. Turn Off and Power Down

    Always disconnect power and gas before servicing. Allow the unit to cool for at least 10 minutes.

  2. Inspect Exhaust Vent for Blockages

  3. Verify Intake Air Supply

  4. Check Flue Pressure Switch and Tubing

  5. Reset and Test

    If error persists, do not continue operating the unit – call a qualified technician.

Parts You May Need

Flue pressure switch tubing
Check Price on Amazon
Flue pressure switch tubing
Check Price on Amazon
Flue pressure switch tubing
Check Price on Amazon
Flue pressure switch tubing
Check Price on Amazon
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When to Call a Professional

If you have cleared all visible blockages, checked pressure switch tubing, and the error persists, contact a Navien-certified technician. Do not attempt to bypass safety devices or disassemble the fan assembly yourself.

Frequently Asked Questions

What does Navien error code 099 mean?
It means high flue gas pressure detected. This is a safety lockout due to improper exhaust or intake airflow.
Can I reset Navien error 099 myself?
Yes, after clearing any blockages and ensuring venting is correct, you can reset by power cycling the unit. But if the error returns, there's an underlying issue.
How do I reset a Navien water heater?
Turn off the power for 30 seconds, then turn it back on. If the unit has a reset button on the control board, press it. Some models require using the remote controller.
What causes high flue gas pressure in Navien?
Common causes include blocked exhaust vent, restricted intake air, failed pressure switch, or damaged pressure switch tubing.
Is it safe to use the water heater with error 099?
No. The error indicates a dangerous condition. Continued use could lead to carbon monoxide poisoning or fire. Turn off the unit and fix the issue.

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