Rinnai Non-SENSEI Code 41
Freeze protection sensor fault. The freeze protection sensor is not reporting correctly. On this generation Rinnai scopes it to external (outdoor) units — the sensor reads outside air, and on indoor Non-SENSEI models it is not in play, which is different from the SENSEI RX/CX where the code applies to every unit. Rinnai also documents that the symptom differs inside the generation: a KB model with the sensor unplugged, cut or shorted will not fire at all, while a VC model will fire and flash code 41 alternating with the set temperature.
Part replacementThe verdict
Replace a part
A sensor and a service call. Worth acting on before a hard freeze rather than after: this is the component the unit relies on to know it needs to protect itself.
Typical cost: $150–$450
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. 44), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- If the sensor is reachable outside the cabinet, check nothing has been packed against it — Rinnai asks that it be open to outside air and not covered with insulation.
- Note whether your unit refuses to fire or fires while flashing the code; Rinnai treats those as different model behaviours and it narrows the diagnosis.
- Book a service call, and treat it as urgent if freezing weather is forecast.
Code 41 on other Rinnai series
Other Rinnai series report code 41 under the same fault name, but each manual is transcribed separately and they do not read alike:
Don't confuse this with
One other Rinnai Non-SENSEI code points at a sensor 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: