Rinnai Non-SENSEI Code 57
Burner overheat bi-metal switch tripped. One of the two bi-metal switches on the rear of the burner has opened. This code exists only on the Non-SENSEI generation. Two things about it are worth knowing: it appears whether or not the unit is running, and it does not clear on its own — the fault has to be corrected first and then power cycled, what Rinnai calls a hard reset. For KB series condensing units Rinnai points to a separate technical bulletin covering codes 14 and 57 together.
Call a proThe verdict
Call a licensed plumber
An overheat safety device at the burner. Rinnai's checks run through gas type, conversion history and manifold pressures before replacing the switch. None of that is homeowner work, and the switch is there to stop something worse.
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. 50), 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.
- Leave the unit off. Power cycling it without fixing the cause simply re-arms a device that has already told you something overheated.
- Find out whether this unit was ever converted between gas types — Rinnai asks it directly for this code.
- Book a licensed professional, and mention the model family: for KB condensing units Rinnai has a dedicated bulletin on codes 14 and 57.
Don't confuse this with
2 other Rinnai Non-SENSEI codes point at a switch 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: