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
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 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: