Rinnai Non-SENSEI Code 05
Bypass flow control device fault. The bypass flow control device — the valve that mixes heated water with water routed around the heat exchanger to hold the outlet temperature steady — is not reporting correctly. On this generation Rinnai gives a shorter procedure than on the SENSEI: cycle the power, run a hot tap, and if code 05 comes back, replace the bypass valve. There are no resistance readings to take first.
Part replacementThe verdict
Replace a part
Worth a power cycle before anything else — Rinnai's own first step, and it costs nothing. If the code survives that, it is a valve replacement with the unit opened and the supplies off, which is a service call.
Typical cost: $0–$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. 10), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Switch the unit off at the wall or the breaker, wait a minute, and switch it back on.
- Run a hot tap and let the heater fire.
- If code 05 comes straight back, the valve itself is the answer — book a service call.
- Look for any sign of water inside the cabinet while you are there. Moisture in a connector produces the same symptom and matters more than the code.
Frequently asked questions
Why does my SENSEI not have a code 05?
It does — but the procedure is different. On the SENSEI, Rinnai goes straight to two resistance readings at connector D and then replaces the device; there is no documented power-cycle step. On the SENSEI RX generation the same component moved to its own number, code 66.
Code 05 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: