Rinnai tankless water heater code 03
Power interruption during bath fill. Code 03 means the same thing on all 3 Rinnai series documented here — but the fix, and what it costs, is still worth reading for your exact unit.
What code 03 means on each Rinnai series
| Series | What it means | Verdict | Typical cost |
|---|---|---|---|
| Non-SENSEI | Power interruption during bath fill | DIY fix | $0–$700 |
| SENSEI | Power interruption during bath fill | DIY fix | $0–$700 |
| SENSEI RX | Power interruption during bath fill | DIY fix | $0–$700 |
Each row opens the full page for that generation. We hold manuals for Non-SENSEI, SENSEI and SENSEI RX, and each one gets its own reading of code 03 — what Rinnai documents, what you can safely check yourself, and what the repair should cost.
What each manual actually says
The table above compares 3 series in four columns, which is enough to route you and not enough to explain anything. This is the Rinnai wording behind each row, one entry per manual, so you can see where the 3 readings of code 03 agree and where they part company.
Non-SENSEI — Power interruption during bath fill
Power to the heater, or the link to its controller, was interrupted part-way through the bath fill function. Nothing has failed. Rinnai assigns this code across all three generations with the same meaning and the same two-press reset, so it is one of the few numbers on this site that does not change with the series.
SENSEI — Power interruption during bath fill
The heater lost power, or lost contact with the controller, part-way through the bath fill function. Nothing has failed: it stops the fill and waits to be reset rather than guessing how much water it already delivered.
SENSEI RX — 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.
Does it matter which Rinnai you have?
Non-SENSEI, SENSEI and SENSEI RX all route code 03 the same way: clear it yourself, at $0–$700. That makes it one of the Rinnai numbers you can act on before working out which unit you own.
What to check first, whatever your series
These checks are on the manufacturer's list for every Rinnai series that reports code 03, so they are safe to work through before you have identified your exact unit. They also cost nothing.
- 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.
That is 3 of the 4 checks documented for code 03. The rest differ by generation, so if none of those explains it, go to your own series above.
Which Rinnai do you have?
On the 3 series that report code 03, the model number on the rating label starts C, RC, RU, RUC and RUR — match yours against the 76 listed below. You can also use the full model-number decoder.
Where this comes from
Source: Rinnai Troubleshooting Tankless Water Heater Diagnostic Codes (100000652) (p. 9), read Aug 2026 — the manufacturer's own documentation for this Rinnai range.
The same number on other brands
Code 03 is not a standard across the industry — every manufacturer publishes its own table. If your unit is not a Rinnai, this number means something else entirely:
Parts, guides and symptoms behind code 03
Code 03 on these 3 Rinnai series points at 1 guide, 1 part and 2 symptoms, each named by the manufacturer's own procedure for this code.