Rinnai LC code (scale build-up): what to do

Rinnai display

LC

“Scale Build-up in Heat Exchanger (when checking maintenance code history, “00” is substituted for “LC”)”

RX, RE/REP, V, RL/VC · SENSEI RX/CX Tech Sheet, p. 1; RE Series Installation and Operation Manual, p. 52; REP Series Installation and Operation Manual, p. 51; Value Series Installation and Operation Manual, p. 35; V53De Installation and Operation Manual, p. 29; VC Series Installation and Operation Manual, p. 38; Troubleshooting Tankless Water Heater Diagnostic Codes, p. 67–68
Owner checks, then technician

Clearing LC after a flush differs by manual: a PC board procedure for a trained and qualified technician (RE manual, p. 52); "reset LC code as instruction" and a call to the Rinnai technical department, with no procedure (REP manual, p. 51); a call to Rinnai technical assistance for PCB reset information (Value manual, p. 38); a board-button reset that the troubleshooting guide says is not in owner manuals (pp. 67–68).

What it means

LC means scale has built up in the heat exchanger and it needs a flush to prevent damage. The display shows LC0 through LC9 Value manual, p. 35. Damage caused by lime build-up is not covered by the warranty RE manual, p. 56; Value manual, p. 38.

The troubleshooting guide explains the number. On newer products, LC locks the heater out. A temporary reset lets it run for 70 hours before it locks out with another LC code, and in the meantime the controller cycles between the set temperature and the LC number; LC2 means three 70-hour periods without a flush pp. 67–68. For Non-SENSEI models, the guide adds that the display alternates between the LC code and the temperature setting and that the controller keeps beeping p. 68.

Check these first

1. To keep hot water until the flush, press On/Off on the temperature controller five times Value manual, p. 35; V53De manual, p. 29; VC manual, p. 38. The RX/CX tech sheet says five times in five seconds p. 1. Repeated LC codes will eventually lock the heater out Value manual, p. 35.
2. Arrange a flush of the heat exchanger. The manuals’ procedure circulates 4 gallons of undiluted, food-grade white vinegar through the heater with a pump for at least 1 hour at 4 gpm (15.1 L/min), then rinses it with water RE manual, p. 56; Value manual, p. 38; V53De manual, p. 32; SENSEI RX Installation and Operation Manual, pp. 67–68. It relies on isolation valves on the water lines, which Rinnai strongly recommends installing RE manual, p. 56. Rinnai’s bulletin TB-181 Higher Vinegar Concentration for Descaling says not to use vinegar solutions stronger than 5% to descale Rinnai products p. 1.
3. If your water is hard, plan for treatment. The LC entry says hard water must be treated to prevent scale build-up or damage to the heat exchanger Value manual, p. 35.

Rinnai lists the flush under maintenance and says repairs and maintenance should be performed by a licensed professional Value manual, pp. 36, 38. The RX manual names a trained and qualified professional SENSEI RX Installation and Operation Manual, p. 64.

When to call a licensed technician

Clearing LC after the flush is where the manuals differ:

• RE: a PC board procedure that the manual says should be performed by a trained and qualified technician RE manual, p. 52.
• REP: the table says only to reset the LC code “as instruction” and to call the Rinnai technical department; the manual prints no clearing procedure REP manual, p. 51.
• Value: after the flush, call Rinnai technical assistance at 1-800-621-9419 for PCB reset information Value manual, p. 38.
• RX: the guide says LC resets on its own if the flush completes properly; if not, a technician uses the A and B switches on the PC board troubleshooting guide, p. 67. The RX manual’s Quick-Flush mode is also started from the PC board, behind the front panel SENSEI RX Installation and Operation Manual, p. 67.
• The guide’s reset for Non-SENSEI models uses the A and B switches too, and the guide says this hard reset is not in the owner or installation manuals p. 68, although the RE manual prints a different board procedure p. 52. On older products, the guide says turning the power off and back on resets LC p. 68.

Every LC table entry also says to call the Rinnai technical department SENSEI RX/CX Tech Sheet, p. 1; RE manual, p. 52; Value manual, p. 35.

Notes for different models

The RU, RUR and RSC tables have no LC. They use SS, a time-based reminder that the installer sets to 0.5, 1 or 2 years or leaves disabled SENSEI RU Installation and Operation Manual, pp. 62, 75. For these SENSEI models, Rinnai’s bulletin TB-188 Optimized Flushing Procedure for SENSEI Tankless Water Heaters changes the flush: 3–4 gpm (11–15 L/min) instead of 4 gpm, a preparation step of unplugging the heater, plugging it in for 20 seconds and unplugging it again (the On/Off button does not do the same), opening the pressure relief valve after the rinse, and discarding the used vinegar pp. 1–2.

The RE manual’s flush adds a step that powers the heater for 20–30 seconds to open the water flow servo RE manual, p. 56.

Related Rinnai codes

• SS “Service Soon (Flush Heat Exchanger)”
• 14 “Heat Exchanger Overheat”
• FF “Maintenance Indicator”

All Rinnai codes

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