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
The same code number can mean something different on another series — make sure you're reading the page for your exact unit:
Don't confuse this with
One other Rinnai Non-SENSEI code points at flame detection too. They are different components in different places, and ordering a part against the wrong one is the most common way this fault gets expensive: