Rinnai SENSEI RX Code 03
Power interruption during bath fill. The unit lost power, or the controller lost contact with it, part-way through the bath fill function. On the SENSEI RX this is a stored fault rather than a broken component: the heater stops the fill and waits to be reset instead of guessing how much water it already delivered.
DIY fixThe verdict
No parts needed — reset or re-check a setting
Nothing on the unit needs replacing yet. Close every hot tap, then reset the heater from the controller. Rinnai's own instruction is to replace the PC board only if code 03 comes back after three resets — so reset first, and only call someone if it keeps returning.
Typical cost: $0–$700
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. 9), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Turn off every hot water fixture in the house, including the tub you were filling.
- Press the ON/OFF button on the temperature controller twice. That clears the code.
- Run a hot tap and confirm the unit fires normally.
- If code 03 returns after three resets, stop resetting it and book a service call — Rinnai points at the PC board at that point, which is a professional replacement.
Frequently asked questions
Do I lose anything by resetting code 03?
No. The reset only clears the fault and returns the heater to normal operation; your temperature setting and parameters are untouched.
Why does the unit care about a power blip during a bath fill?
Bath fill meters a set volume of water into the tub. If power drops mid-fill the heater can no longer be sure how much it has delivered, so it stops and flags the interruption instead of over- or under-filling.
It came back three times. Is that a $700 repair?
Not necessarily, but it is now a service call. A PC board is the most expensive outcome in that range; a loose connector or a failing outlet is cheaper and gets ruled out first.