Rinnai Non-SENSEI Code 72
Flame rod fault. The flame rod — the sensor that confirms there is actually a flame — is not reporting properly. Rinnai checks the wiring, whether the rod is touching the flame when the unit fires, carbon build-up on the rod, and the current it produces, which must hold at least one microamp. If the rod and gasket do not fix it, the list continues to a leaking heat exchanger and then the PC board.
Call a proThe verdict
Call a licensed plumber
Often the cheapest of the gas-side faults: a flame rod and its gasket are inexpensive. But it is a flame safety device on a gas appliance, so replacing it is a professional job, and Rinnai's list ends somewhere much more expensive if the rod is sound.
Typical cost: $150–$600
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. 60), 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.
- Note whether the unit lights and then drops out, or never lights at all — that distinction helps separate this from code 11.
- If you smell gas, leave and call your gas utility from outside.
- Book a licensed professional. The gasket must be replaced whenever the flame rod is removed, which is one reason this is not a DIY part.
Code 72 on other Rinnai series
Rinnai keeps the same fault name for code 72 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: