Water Heater Error Code Flashing or Blinking

Something on the unit is blinking, flashing, or displaying a code you don't recognize — before you can act on it, you need to know which brand's display convention you're looking at, since the same digits or flash count mean different things on different units.

Most likely causes, ranked

• You're looking at a real fault code, and it's brand-specific. Rinnai and Rheem tankless models show a short numeric code (like Rinnai 11 or Rheem 11) directly on a digital display. Navien models show a letter-and-number code such as Navien E003. AO Smith gas tank models with no digital display instead blink the gas control valve's status light in a counted pattern, like 6 Flashes or 2 Flashes — you have to count the blinks between pauses to get the code.
• It's a maintenance warning, not a shutdown. Some codes, like Rinnai's LC (scale build-up), alternate with the normal temperature display and the unit keeps running — it's telling you maintenance is due, not that anything has failed yet.
• It's a safety lockout that will keep returning until the cause is addressed. Codes tied to overheat limits, flame-failure, or flammable-vapor sensors are designed to keep tripping if the underlying condition — scale, blocked venting, stored solvents near the unit — isn't fixed. Resetting the code without fixing the cause just delays the next lockout.
• The display itself is glitching. Less common, but a control-board or display fault can occasionally show a garbled or flickering readout rather than a clean code — a full power cycle usually clears a genuine display glitch, while a real fault code returns.

Check this first

1. Write down the exact code or count the flash pattern carefully — for flash codes, count the blinks in one group before the pause repeats, since miscounting by one changes the meaning entirely.
2. Confirm which brand and model you have — check the data plate or panel for the manufacturer name and series, since the same two digits mean different things across brands.
3. Note whether the unit still runs (a warning code) or has stopped producing hot water (a lockout or shutdown code) — that difference changes how urgent the fix is.
4. Look up the exact code using the brand and code you found rather than guessing from a similar-looking one.

Which fault code are you seeing?

Look it up directly: code lookup searches every documented code on this site by brand and by the code or flash count itself, or jump straight to a brand's full list: Rinnai, Navien, Rheem, AO Smith.