Quick answer
Navien error 003 means ignition failure: the unit tried to light and did not detect a flame. Check that the gas valve is open, other gas appliances work, and a propane tank is not empty. Clear snow or debris from the intake and exhaust vents, and check that the condensate drain is not blocked. Reset by turning the power off and on. If 003 keeps returning, the gas pressure, igniter, flame rod or gas valve needs a technician. Call (888) 217-6781 to reach a plumbing company taking calls in your ZIP.
Follow the short menu, then your 5-digit ZIP. The line goes quiet for a few seconds while it connects; stay on. If it does not connect, call once more: companies taking calls change minute to minute.
Written & reviewed by Marcus ReedIICRC WRT
Reviewed November 4, 2026· Next review May 2027
Navien tankless water heaters and combi boilers display a numbered error when they stop. Error 003 is ignition failure, the most common one after a gas or venting interruption.
Check These First
- 1The gas valve below the unit is open.
- 2The gas supply. If other gas appliances do not light, contact the gas utility.
- 3Propane. Check the tank gauge.
- 4The vents. Intake and exhaust terminals must be clear; snow and nests are common culprits.
- 5The condensate drain. Navien units are condensing; a blocked drain or trap can affect operation.
- 6Reset by power cycling the unit, then try a hot tap.
If It Keeps Coming Back
| Cause | What it needs |
|---|---|
| Low gas pressure or undersized line | Pressure test by a technician |
| Dirty or failed flame rod | Cleaning or replacement |
| Failed igniter | Replacement |
| Gas valve fault | Replacement |
| Venting problem | Inspection |
Talk to a plumber about this
One call reaches a plumbing company taking calls in your ZIP.
Safety
If you smell gas, leave and call the gas utility from outside. CPSC recommends carbon monoxide alarms on every level of a home with gas appliances.
The Call
Call when 003 returns after the gas and vents check out. See Rinnai code 11 for the same fault on Rinnai units. (888) 217-6781 connects you to a plumbing company taking calls in your ZIP. Follow the short menu, enter your 5-digit ZIP and stay on while it connects; if it does not connect, call once more, because the companies taking calls change minute to minute.
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Frequently Asked Questions
What does error 003 mean on a Navien?
Ignition failure: the burner did not light, or the flame was not detected, after the unit tried to ignite.
How do I reset a Navien error 003?
Turn the unit's power off and back on, or press the reset button on the front panel if your model has one, after checking the gas and vents.
Can a clogged condensate drain cause Navien error 003?
It can contribute. A blocked condensate line can back water into the unit and affect combustion; clearing it is a good check.
Sources
- Navien support
- U.S. Department of Energy: tankless or demand-type water heaters
- U.S. Consumer Product Safety Commission: carbon monoxide information
Methodology: How we source and verify data · Report an error
Disclaimer: HearthDry is an independent educational resource. This article is for informational purposes only and does not constitute professional, legal, or insurance advice. Consult licensed professionals before making decisions about your property or insurance claims.
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