Rinnai LC Code: Scale Buildup

Rinnai’s LC (or LC1) code is a maintenance reminder rather than a fault: the heat exchanger has accumulated enough mineral scale that a descaling flush is due. Ignoring it repeatedly can lead to reduced output and, eventually, real error codes.

Illustration of mineral scale flakes collected in a tray next to a small descaling pump and hose.

Likely Causes, Ranked

Normal mineral scale accumulation
Hard water areas hit this reminder much sooner than soft-water areas.

Step-by-Step Diagnosis

DIY SAFE
Schedule a descaling flush

See our full flush guide for the isolation-valve procedure and descaling solution to use.
DIY SAFE
Clear the code per your model’s manual

Usually a specific button-hold sequence after the flush is done.

FAQ

Is the LC code an emergency?

No — it’s a scheduled-maintenance reminder. Plan a flush in the next few weeks, don’t panic.

Written by HotWater Decoded — water heater repair specialists. Technically reviewed by a licensed technician on our team.

Sources

Rinnai maintenance-interval documentation, consistent with LC/LC1 conventions across tankless brands