Rinnai LC Error Code: Scale build-up in heat exchanger
Updated October 2026 · Sourced from Rinnai documentation
🧭 Check a few things first
Scale has built up in the heat exchanger. The sheet says to flush the heat exchanger and replace it if needed. In code history, 00 is shown in place of LC.
Is it safe to keep running? Check the steps below first. Have a qualified professional flush the heat exchanger. If it cannot be restored, the sheet says to replace the heat exchanger.
LC at a glance
| Code / how it shows | Meaning | Applies to |
|---|---|---|
| LC Code shown on the temperature controller display | Scale build-up in heat exchanger | RL75i (VB2528FFUD-US) and RL94i (VB2735FFUD-US) tankless water heaters |
Check this first
Only steps a homeowner can do safely. Do not open electrical panels or the burner area.
- The unit may still run. Follow the flushing instructions in your manual or have a professional do it.
- Clean the inlet water supply filter (the sheet's No Code item lists it).
🛑 Stop and call a licensed pro if
- Have a qualified professional flush the heat exchanger. If it cannot be restored, the sheet says to replace the heat exchanger.
- You smell gas. Leave the house, do not touch switches, and call your gas utility from outside.
- Codes for flame failure, overheating, venting or the control board that return after one reset.
- Water leaking from the heater, the relief valve discharging, or scorching around the burner area.
- A carbon monoxide alarm sounds. Get everyone outside and call 911 or the fire department.
Safe first steps for any Rinnai code
- Write down the exact code shown on the controller or the number of status light flashes.
- Turn the water heater power off and back on (or press the reset button the manual describes) once. If the code comes back, stop resetting.
- Make sure the gas supply valve to the heater is open and other gas appliances in the home are working.
- Make sure the cold water supply valve is fully open and hot water taps are not partly closed.
- Look at the outside vent terminal for snow, ice, leaves or anything blocking it (look only).
Source: Rinnai RL75i / RL94i Quick Reference sheet U287-1817x01(00), Error Codes. Codes are series-specific, so your unit's own manual is the final word. Reviewed October 2026.
Ryan Giles · Red Seal Certified Plumber · Ask a plumber · Ask an HVAC technician
Related Rinnai codes
02 : No burner operation during freeze protection mode31 : Burner sensor error73 : Burner sensor circuit error03 : Power interruption during bath fill05 : By-pass flow control10 : Air supply or exhaust blockage, or condensate trap full11 : No ignition12 : No flame14 : Heat exchanger overheat15 : Venturi control16 : High outgoing temperature17 : Venturi blockage