Rinnai SENSEI RX Code 15
Venturi control fault. The PC board is not getting the response it expects from the venturi control on the gas valve — the assembly that meters the air-to-gas ratio. On the SENSEI RX, Rinnai's first check is a reed switch on the back of the gas valve sitting out of position, then the gas valve and solenoid wiring, then the fan motor and airflow through the vent.
Call a proThe verdict
Call a licensed plumber
One free thing to try first: Rinnai's step one is a full power reset of the heater. If the code returns, this is a gas valve and venturi diagnosis with resistance readings taken at the PC board, and it ends in replacing the gas valve assembly or the fan motor — professional work on the gas train either way.
Typical cost: $0–$1,100
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 SENSEI RX — not averaged across the brand.
Source: Rinnai Troubleshooting Tankless Water Heater Diagnostic Codes (100000652) (p. 26), 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.
- Reset the main power to the heater: switch it off at the breaker, wait a minute, switch it back on.
- If the code comes straight back, leave the unit off and book a licensed professional.
- If you smell gas at any point, leave and call your gas utility from outside.
Frequently asked questions
Does code 15 exist on older Rinnai units?
Not on the non-SENSEI generation. Rinnai lists code 15 for the SENSEI and SENSEI RX/CX series only — it belongs to the gas valves that actively control the air-fuel ratio.
Why would a reset ever fix a hardware fault?
It does not fix hardware. It clears a fault latched from a one-off condition — a brownout, a momentary signal loss. If the hardware is genuinely wrong, the code returns immediately.