Rinnai Rinnai RL94iN RL Series Tankless Water Heater LC Error Fix: Scale Buildup — Maintenance Required

Error code LC on the Rinnai Rinnai RL94iN RL Series Tankless Water Heater means: Scale Buildup — Maintenance Required. The unit is indicating that periodic descaling maintenance is due. LC is not an error code but a maintenance reminder that appears after a preset number of operating hours (typically 500 or 1,000 hours of burner operation, depending on the model and configuration). Hard water (water with high mineral content — calcium, magnesium, lime) causes scale deposits to accumulate inside the heat exchanger over time. Scale acts as an insulator, reducing heat transfer efficiency and restricting water flow. If left unaddressed, scale buildup leads to declining performance, higher gas consumption, error codes 14 (thermal fuse), 16 (over temperature), 41 (abnormal temperature rise), and ultimately heat exchanger failure. To service: (1) Close the gas supply and hot/cold isolation valves. (2) Connect a submersible pump and two hoses between the service valves (or cold water inlet and hot water outlet). (3) Fill a 5-gallon bucket with white vinegar or commercial tankless descaler solution. (4) Circulate the solution through the heat exchanger for 45-60 minutes. (5) Flush with clean water to remove descaler residue. (6) Open the isolation valves and restore gas supply. (7) Reset the LC counter by pressing the appropriate button combination (varies by model — consult the manual). In hard water areas (above 7 grains per gallon), descale annually. In moderate water, every 2-3 years. Consider installing a whole-house water softener or a scale prevention system to extend maintenance intervals.

The most successful fix is "Perform a Professional Heat Exchanger Descale and Inspection" (hard difficulty, ~90 minutes). Estimated DIY cost: $10-$25. HomeMD has 2 community-ranked fixes for this error.

This error is rated info severity. It is generally not urgent and can often be resolved with a simple DIY fix.

Yes — the top-ranked community fix ("Perform a Professional Heat Exchanger Descale and Inspection") is rated hard difficulty and takes about 90 minutes. Tools needed: Adjustable wrench, Submersible pump, Two garden hoses, Multimeter, Flashlight.

DIY cost: $10-$25. Professional repair typically costs $150-$300. Many homeowners save money by trying the top-ranked community fix first.

The Rinnai Rinnai RL94iN RL Series Tankless Water Heater has 8 other known error codes, including: 02 (Ignition Failure), 03 (Bath Fill Function Abnormality), 05 (Blocked Exhaust / Air Supply), 10 (Blocked Exhaust — Air Pressure Switch), 11 (No Ignition), and 3 more.

Error code LC also appears on 8 other Rinnai models: Rinnai RE180iN RE Series Non-Condensing Tankless Water Heater, Rinnai RL75iN RL Series Tankless Water Heater, Rinnai RSC160iN Condensing Combi Boiler, Rinnai RU130iN Sensei Super High Efficiency Plus Tankless Water Heater, Rinnai RU199iN Sensei Super High Efficiency Plus Tankless Water Heater, Rinnai RUR199iN Sensei Recirculating Tankless Water Heater, and 2 more. The fix may vary by model, so check each model's specific page for tailored repair steps.