Rinnai Non-SENSEI Code 79
Water leakage detected. The leak detector in the bottom of the cabinet has been triggered. This code exists only on the Non-SENSEI generation. Rinnai's sequence is the harness, then the heat exchanger and all internal piping, then the bottom pan for pooled water, and only after all of that does it consider that the sensor itself has failed.
Call a proThe verdict
Call a licensed plumber
Water and mains electricity in the same cabinet. Switch it off and call someone — the cheap outcome is a failed sensor, the expensive one is a leaking heat exchanger, and you cannot tell which from outside.
Typical cost: $150–$1,600
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. 62), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Switch the unit off at the breaker. Do not run it to see whether the code clears.
- Close the cold water isolation valve to the unit if you can reach it safely.
- Look for water on the floor under the unit and for staining on the wall behind it, and tell the technician what you found.
- Book a licensed professional. A leak inside a gas appliance with live electronics is not something to keep operating.