Rinnai Tankless Water Heater Error Code LC: Meaning & How to Fix It

By the ErrorCodePro Editorial Team · Last reviewed October 20, 2026

Rinnai tankless water heater error code LC means: Scale is building up in the heat exchanger. On non-SENSEI models, LC0–LC9 are the only codes that let the heater keep running, and the display alternates with the temperature. [1] Keep using it? Yes, temporarily. Flush soon to avoid damage. Start with the owner checks below, beginning with: flush the heat exchanger.

Smell gas? Leave the building now. Do not touch light switches, phones or appliances inside. Call your gas utility or 911 from outside. CO alarm sounding or headache, dizziness or nausea? Get everyone outside and call 911. Gas valves, burners, venting and wiring are for a licensed technician only. See our safety policy.

Quick facts

Code	LC
Also shown as	LC0, LC1, LC2, LC3, LC4, LC5, LC6, LC7, LC8, LC9
Brand / appliance	Rinnai tankless water heater (sensei and non-sensei tankless water heaters)
System	Heating
Official meaning	Scale is building up in the heat exchanger. On non-SENSEI models, LC0–LC9 are the only codes that let the heater keep running, and the display alternates with the temperature. [1]
Keep using it?	Yes, temporarily. Flush soon to avoid damage
DIY-safe?	Owner checks only (listed below)
Support	Rinnai support, 1-800-621-9419

On this page: Meaning · Steps · Parts · When to call a technician · Related codes · FAQ

What error code LC means on a Rinnai tankless water heater

Scale is building up in the heat exchanger. On non-SENSEI models, LC0–LC9 are the only codes that let the heater keep running, and the display alternates with the temperature. [1]

This is a heating code. Codes and wording can vary by model, so check your owner's manual for your model number.

How to fix Rinnai tankless water heater error code LC (safe owner checks)

Owner checks only: on heating, cooling and water-heating equipment, limit yourself to reading the code and checking the thermostat, breaker and service switch, air filter, condensate drain, that the gas supply valve is open (no disassembly) and that vent terminals are clear of snow or debris. Reset power only if your manual allows it.

Safety first: disconnect power before you remove any panel or reach into the sump or drum. Do not touch wiring, the control board or the motor. If you see water near electrical parts, stop and call a technician. These steps are based on Rinnai's published guidance [1], rewritten for clarity.

Flush the heat exchanger. Flush it per the procedure in your owner's manual, or have a plumber do it.
Temporary use. Pressing the on/off button five times lets it run temporarily for up to about 70 hours.
Prevent. Treat hard water to prevent scale.

Parts that may be involved

Exact parts depend on your model number. This page lists part types only, never part numbers.

No specific part is implied by the manufacturer's guidance for this code.

When to call a technician

The LC count reset after flushing uses a board procedure: technician
Gas pressure, gas valve, igniter, flame rod, venting or combustion problems: licensed plumber or gas technician
Gas valves, burners, igniters, flame sensors, venting/flue or CO concerns: licensed HVAC technician or plumber
Refrigerant work: EPA 608-certified technician only
Smell of gas: leave and call the gas utility or 911
Anything involving wiring, the control board, the motor or the water valve electrics
The appliance is under warranty: contact Rinnai support, 1-800-621-9419 first

Frequently asked questions

What does error code LC mean on a Rinnai tankless water heater?

Rinnai lists LC as follows: Scale is building up in the heat exchanger. On non-SENSEI models, LC0–LC9 are the only codes that let the heater keep running, and the display alternates with the temperature.

Is it safe to keep using the tankless water heater with LC?

Yes, temporarily. Flush soon to avoid damage.

Can I fix Rinnai tankless water heater error LC myself?

Only with the owner checks on this page, starting with: flush the heat exchanger. If it persists, call a technician or Rinnai support, 1-800-621-9419.

Is LC0 the same as LC?

Yes. Rinnai's documentation lists LC0, LC1, LC2, LC3, LC4, LC5, LC6, LC7, LC8, LC9 with the same meaning as LC; the display format depends on the model.

Sources

https://media.rinnai.us/salsify_asset/s-3e3cd69f-0edc-4b85-8d6d-93b39057fab5/100000652-Troubleshooting%20TWH%20Diagnostic%20Codes.pdf (official)

Last reviewed: October 20, 2026. ErrorCodePro is not affiliated with Rinnai.