Rinnai Non-SENSEI Code LC
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.
Also displayed as: 00, LC0, LC1, LC2, LC3, LC4, LC5, LC6, LC7, LC8, LC9
DIY fixThe verdict
Descale the unit
The cheapest verdict on the site, and the one most worth acting on. A descale kit and citric acid is roughly $30 to $80 of supplies, or a service call if you would rather not. Ignoring it is how a heat exchanger — the most expensive part on the unit — gets destroyed.
Typical cost: $25–$300
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. 67), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Flush the heat exchanger. Our step-by-step descaling guide covers the whole job.
- Clean the inlet water filter while the unit is isolated — it is two minutes and it is already open.
- If you need hot water before you can flush it, Rinnai documents a temporary reset: press the controller's on/off button five times. The unit runs about 70 more hours and then locks out again with the next LC number.
- If your water is hard, treat it. Rinnai is explicit that hard water must be treated or the heat exchanger will be damaged.
Frequently asked questions
My unit still makes hot water. Can I ignore LC?
It will keep running — Rinnai says LC codes are the only ones that allow that, which is exactly why they get ignored. The digit after LC is counting how many times you have postponed the flush, and the thing being protected is the heat exchanger, the most expensive part on the unit.
Why does my newer Rinnai show SS instead of LC?
They are different indicators. SS is a time-based service reminder set at installation, and Rinnai lists it for the SENSEI and SENSEI RX/CX series only. LC is an actual scale detection, and on the Non-SENSEI generation it is what you get instead.
Code LC 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: