Code 10 is about air. A tankless heater needs a clear path for combustion air in and exhaust out, and anything that interferes can stop it from running.
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.
Causes Rinnai lists for code 10
- A blocked flue inlet or exhaust.
- Vent materials that are not approved for the unit.
- Poor vent connections.
- A vent run that is too long.
- Incorrect DIP switch settings.
- A blocked fan.
What you can safely check
- Outside vent terminations are free of leaves, nests, plants, stored items or anything stacked against them.
- Nothing is blocking airflow around the heater itself.
When to call a plumber
If the vents are clear and the code persists, or appeared right after installation, call a licensed plumber. Vent materials, length and connections, DIP switches and the fan are technician work.
General information, not professional or legal advice; follow your manufacturer's manual, and your installer and local permit office have the final word. Sources:Rinnai RL75i/RL94i technical sheet (diagnostic codes); Rinnai, Troubleshooting Tankless Water Heater Diagnostic 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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