Rinnai tankless water heater code LC
Your series decides which reading applies. Across the 2 Rinnai series documented here, code LC is listed as scale build-up in the heat exchanger (1 series) and scale build-up lockout (1 series). Find your series in the table below, where those readings route to a descale.
What code LC means on each Rinnai series
| Series | What it means | Verdict | Typical cost |
|---|---|---|---|
| Non-SENSEI | Scale build-up in the heat exchanger | DIY fix | $25–$300 |
| SENSEI RX | Scale build-up lockout | DIY fix | $25–$300 |
Each row opens the full page for that generation. We hold manuals for Non-SENSEI and SENSEI RX, and each one gets its own reading of code LC — what Rinnai documents, what you can safely check yourself, and what the repair should cost.
What each manual actually says
The table above compares 2 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 2 readings of code LC agree and where they part company.
Non-SENSEI — Scale build-up in the heat exchanger
Scale has built up in the heat exchanger and it needs flushing. Rinnai notes that these are the only codes that let the water heater keep running: the display alternates between the LC code and the set temperature, and the controller keeps beeping. The digit counts your postponements — LC2 means the unit has been reset for three 70-hour periods without an actual flush. In the code history, "00" is substituted for "LC". On older Non-SENSEI products the code clears with a power cycle; on newer ones there is a lockout, and after flushing the reset is the two buttons on the PC board held together.
SENSEI RX — Scale build-up lockout
The heater has detected lime scale in the heat exchanger and is counting down to protecting itself. Rinnai displays this as LC, as LC0 through LC9, or as 00 when you read it back in the maintenance code history. The digit is a counter: each temporary reset buys 70 hours of operation, and LC2 means the unit has been reset for three of those 70-hour periods without an actual flush.
Does it matter which Rinnai you have?
Non-SENSEI and SENSEI RX all route code LC the same way: a descale, at $25–$300. That makes it one of the Rinnai numbers you can act on before working out which unit you own.
Which Rinnai do you have?
On the 2 series that report code LC, the model number on the rating label starts C, RC, RU, RUC and RUR — match yours against the 68 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. 67), read Aug 2026 — the manufacturer's own documentation for this Rinnai range.
Parts, guides and symptoms behind code LC
Code LC on these 2 Rinnai series points at 5 guides, 2 parts and 3 symptoms, each named by the manufacturer's own procedure for this code.