Noritz tankless water heater error 10
Your Noritz tankless water heater shows code 10. Noritz calls it an early warning, so act on it before it turns into code 90.
Combustion abnormality: an early warning before the more serious code 90.
What 10 means on Noritz
Noritz says error code 10 indicates a combustion abnormality and is usually a precursor to the more severe code 90. Noritz lists three groups of causes: wrong installation settings, low air flow, and low gas flow or pressure. All of them stop the unit producing the right hot-water temperature.
Step-by-step fix
Check the vent terminals
Outside, check the intake and exhaust terminals for snow, leaves, nests or debris and clear them safely.
Reset by power
Noritz: disconnect and reconnect the power. If "908" is displayed, an internal lock is active and the error cannot be reset by the owner.
Book a licensed contractorCall a pro
If 10 returns, a licensed contractor should verify the elevation, vent type, vent length, vent size and common-vent settings and the inlet gas pressure, as Noritz describes. Noritz technical assistance: 866-766-7489.
Common causes
- Incorrect installation settings (elevation, vent type, vent length, vent size, common vent)
- Low air flow: incorrect venting, dirty or clogged terminations or filters
- Low gas flow or heating value: gas line too small or too long, gas meter too small
- Low primary gas pressure
How to prevent it
- Keep vent terminations and filters clean
- Make sure the installer set elevation and vent settings to match your installation
Tools & parts you may need
- Gloves, torch and a soft brush
Related Noritz codes
| Code | Meaning (from Noritz) |
|---|---|
| 90 | Combustion abnormality: more severe, same checks; contractor needed |
FAQ
What is the difference between Noritz code 10 and 90?
Noritz describes 10 as the early warning and 90 as the more severe combustion fault. The troubleshooting is the same, but 90 needs a licensed contractor.
Can I keep using hot water with code 10?
The unit may still work, but Noritz treats 10 as a warning of more severe problems. Fix the airflow soon.
Sources
Checked on 26 October 2026. Codes can differ between model generations: your own manual always wins. Spotted an error? See About & corrections.