Rinnai Non-SENSEI Code 12
Flame failure. The burner lit and then the flame was lost or stopped being detected. Rinnai prints one checklist for all three generations here: gas turned on and present, a flame rod and electrode tight in the bracket, inlet gas pressure held with every gas appliance in the building firing, and then vent clearances and equivalent length, because exhaust recirculating back into the intake causes incomplete combustion and a code 12.
Call a proThe verdict
Call a licensed plumber
Gas supply, the flame sensing circuit, or combustion air. All three are professional work on a gas appliance. Check the supply, then stop.
Typical cost: $150–$900
US estimate for parts and labor. Prices vary by region and by who does the work — see how we estimate costs.
What the manual says
The meaning above is transcribed from the manufacturer's diagnostic documentation for the Non-SENSEI — not averaged across the brand.
Source: Rinnai Troubleshooting Tankless Water Heater Diagnostic Codes (100000652) (p. 20), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
Before anything else: if you smell gas, stop here, leave, and call your gas utility.
- Check another gas appliance works, and check the propane tank gauge if the unit runs on propane.
- Go outside and confirm nothing is blowing into or blocking the vent terminal.
- If you smell gas, leave and call your gas utility from outside — do not restart the unit.
- Book a licensed professional. The flame rod, the gas valve and the inlet pressure all need instruments to check.
Code 12 on other Rinnai series
Rinnai keeps the same fault name for code 12 on some series and not others. Check the one that matches your rating label:
Don't confuse this with
One other Rinnai Non-SENSEI code points at flame detection too. They are the same symptom reported from a different place in the unit, so which one the display shows is what tells you where to look: