Rinnai · Water heater
LC (LC0–LC9) Scale buildup warning
What this code means
The unit has detected scale accumulation in the heat exchanger and is warning before it causes damage.
Most likely causes
- Hard water without a softener or descaling routine
- Overdue annual flush
What to try first
Push the On/Off button on the controller 5 times within 5 seconds to temporarily continue operating, but schedule a heat exchanger flush soon — repeated LC codes eventually lock the unit out.
Good news: this one is often fixable without a service call. If it persists after the steps above, have it looked at.
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What does Rinnai error code LC (LC0–LC9) mean?
Scale buildup warning. The unit has detected scale accumulation in the heat exchanger and is warning before it causes damage.
Can I fix Rinnai code LC (LC0–LC9) myself?
Often, yes. Push the On/Off button on the controller 5 times within 5 seconds to temporarily continue operating, but schedule a heat exchanger flush soon — repeated LC codes eventually lock the unit out.
What causes Rinnai code LC (LC0–LC9)?
The most common causes are: hard water without a softener or descaling routine; overdue annual flush.
Other Rinnai water heater codes
All Rinnai water heater error codes →
Other water heater brands: Rheem · Ruud · Navien · Noritz · Takagi · A.O. Smith · Bradford White · State / American · Generic electric · Generic tankless
This information may contain errors or not apply to your exact model — always double-check it against your appliance's own manual before acting. If there's any chance of a gas, fire, electrical, carbon monoxide, or other safety hazard, stop and call a licensed professional or the appropriate agency (e.g. your gas utility) instead of relying on this page alone.