Can I fix Rinnai code LC myself?

Start with these safe checks: To run temporarily, press the on/off button on the controller 5 times within 5 seconds. It runs about 70 hours before locking out again, and the number after LC counts the resets. Flush the heat exchanger following the owner's manual, or have a plumber do it. Hard water should be treated. Don't keep resetting without flushing; scale damage to the heat exchanger isn't covered.

When should I call a technician for code LC?

Don't keep resetting without flushing; scale damage to the heat exchanger isn't covered. Smell gas? Leave right away, don't touch light switches or phones inside, and call your gas utility or 911 from outside. Never open a gas valve, burner, gas line, vent or flue connection, or bypass a safety switch. Repeated lockouts, scorching, soot, or a CO alarm mean shut it off and call a licensed gas technician.

Rinnai Tankless Water Heater Error Code LC / LC0 / LC1: Scale…

What LC means

Scale is building up in the heat exchanger and it needs to be flushed. These codes lock the heater out to prevent damage.

Also shown as: LC0, LC1, LC2, LC9, 00, depending on the model.

Likely causes

Hard water
Overdue flushing

Safe first checks

To run temporarily, press the on/off button on the controller 5 times within 5 seconds. It runs about 70 hours before locking out again, and the number after LC counts the resets.
Flush the heat exchanger following the owner's manual, or have a plumber do it. Hard water should be treated.

When to stop

Don't keep resetting without flushing; scale damage to the heat exchanger isn't covered.

Checked against: Rinnai: Troubleshooting Tankless Water Heater Diagnostic Codes (100000652). Codes can differ by model and year, so confirm with your owner's manual.