Code 90 is about the balance of gas and air. Noritz separates likely causes by whether the heater is new or has been running for years.
Safety first
If you smell gas, do not light anything or touch electrical switches. Leave the house and call SDG&E or 911 from outside. Manufacturers reserve gas, burner, venting and internal electrical work for qualified technicians.
Common causes
- New installs: low gas pressure, venting problems or incorrect DIP switch settings.
- Older units: dirt or lint, a blocked intake or exhaust termination, and buildup on the burner, fan or heat exchanger.
What you can safely check
- Clear leaves, lint or debris from the outside intake and exhaust terminations and the intake area on the unit's cover.
When to call a plumber
Gas pressure, settings and cleaning the burner, fan or heat exchanger are jobs for a licensed contractor.
General information, not professional or legal advice; follow your manufacturer's manual, and your installer and local permit office have the final word. Sources:Noritz Help Center, Error Code 90; Noritz, Common Noritz Tankless Error Codes. SD Water Heaters is not affiliated with any manufacturer; brand names are used only to identify products, and codes can differ by model, so confirm in your own manual.
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