Rinnai Tankless Water Heater Error Codes: Complete Troubleshooting Guide & Fault Directory
A flashing digital code on your Rinnai tankless water heater controller means the internal diagnostic computer has detected an operating fault and shut down the burner to safeguard your home. While some codes require an immediate call to a licensed technician, others can be resolved with basic maintenance like cleaning an intake filter or checking a gas shut-off valve.
This troubleshooting and error code directory blog is provided by All Hot Water LLC, Seneca, South Carolina's dedicated water heater installation, replacement, and repair specialists. Whether you are living along Lake Keowee or right in Seneca, this guide will help you diagnose what your Rinnai unit is telling you, how to address the most frequent issues, and when to call in a professional.
The 3 Most Common Rinnai Tankless Fault Codes (Causes & Solutions)
Out of all diagnostic codes, three appear far more frequently than any others: Code 11, Code 12, and Code LC (or 55/SS).
1. Code 11: No Ignition (Ignition Failure)
What it means: The water heater attempted to light the burner during an open-tap call for hot water, but failed to establish a stable flame.
Primary Causes:
The main gas valve feeding the water heater, gas meter, or propane tank is partially or fully closed.
Air pockets in new gas lines or empty propane fuel tanks.
Insufficient inlet gas pressure caused by an undersized supply line or regulator failure.
Carbon buildup or white oxidation deposits on the ceramic spark igniter or flame rod.
Obstructed or unseated exhaust/intake venting pipe.
Likely Solutions:
Check Your Gas Supply: Ensure your gas valve is parallel to the pipe (fully open) and check that other gas appliances in the home are firing correctly.
Inspect the Flame Rod & Igniter: Turn off electrical and gas power, remove the flame rod assembly, and inspect for carbon accumulation. Clean carefully with very fine abrasive cloth. Note that the mounting gasket must be replaced if broken or damaged.
Verify Gas Pressure: A licensed plumber must connect a manometer to ensure dynamic inlet gas pressure meets rating plate specifications under full high-fire load.
2. Code 12: Flame Failure
What it means: The water heater successfully ignited, but the flame sensor lost the flame signal during operation, triggering an automatic safety shutdown.
Primary Causes:
Supply gas pressure drops while the unit ramps up to high fire (often due to an undersized meter, line, or tank regulator).
A dirty, loose, or oxidized flame sensor rod failing to read micro-amp rectification current.
Exhaust gas recirculation entering the intake terminal outside the home.
Loose electrical ground wire or reverse electrical polarity.
Likely Solutions:
Clean and Reseat Flame Rod: A loose flame rod (known as a "floating flame rod") causes intermittent flame loss. Tighten the bracket and ensure the silicone protective sleeve has no cracks.
Check Outdoor Vent Clearances: Confirm outdoor concentric or twin-pipe exhaust terminals are unobstructed by vegetation, debris, or roof overhangs that force flue gases back into the air intake.
Regulator Distance Verification: Two-stage inlet gas regulators must be located at least 6 feet away from the water heater to avoid pressure pulsation and bleed-through.
3. Code LC / LC0–LC9 (or SS / 55): Lime / Scale Build-Up in Heat Exchanger
What it means: The unit has detected mineral scale accumulation (calcium and magnesium) inside the heat exchanger tubing, creating heat transfer restrictions. On SENSEI™ models, Code SS (displayed as 55) is a programmed service-interval alert.
Primary Causes:
Hard municipal or well water baking mineral scale onto internal heat exchanger walls over months or years of use.
Lack of routine annual vinegar descaling maintenance.
Likely Solutions:
Flush the Heat Exchanger: Isolate the cold and hot service isolation valves, connect a submersible pump kit with 4 gallons of food-grade virgin white vinegar or an approved descaling chemical, and circulate through the heat exchanger for 45 to 60 minutes.
Reset Code LC: On newer non-SENSEI units, press the On/Off button on the controller 5 times for a temporary 70-hour operational bypass. For a permanent hard reset after flushing, simultaneously press and hold the internal PC board buttons A and B for 5 seconds.
Reset Code SS (55): Press the On/Off button on the controller 5 times within 5 seconds.
Long-Term Protection: Install an upstream whole-home water softening or scale prevention filter to avoid premature heat exchanger perforation.
Comprehensive Rinnai Tankless Error Code Directory
Below is the complete fault index and diagnostic definitions for Rinnai residential and commercial units:
Error Code | Primary Description | What It Means & Primary Diagnostic Area |
02 | No Burner Operation During Freeze Protection | Burner failed to fire during automated anti-freeze cycle; verify gas supply, gas pressures, igniter, and flame rod. |
03 | Power Interruption During Bath Fill | Electrical power was interrupted during an automated bath-fill cycle; reset controller twice. |
05 | Bypass Flow Control Device | Mechanical or electrical fault with the internal bypass water flow control valve. |
07 | Circulation Flow Rate Below 2.1 GPM | Water flow dropped below 2.1 GPM on hybrid RH180 units; check circulation pump, supply pressure, and filters. |
10 | Air Supply, Exhaust Blockage, or Condensate Trap Full | Flue gas exhaust or air intake restriction, blocked venting, dirty air filter, or backed-up condensate trap. |
11 | No Ignition | Water heater fails to ignite upon call for hot water; inspect gas valves, gas pressure, igniter gap, and flame rod. |
12 | Flame Failure | Flame extinguished after ignition; check gas line sizing, gas pressure drop, flame sensor, and venting recirculation. |
13 | Combustion Fault | Incomplete combustion on Non-SENSEI models; verify 4-inch B-Vent, room combustion air, and high/low manifold pressures. |
14 | Thermal Fuse or Overheat Sensor (ODS) | Heat exchanger bi-metal overheat switch opened or thermal wrap fuse blew due to extreme internal heat or scaling. |
15 | Venturi Control Device | Venturi control malfunction or stepper motor circuit anomaly on SENSEI™ models; verify fan and gas valve assembly. |
16 | High Outgoing Water Temperature | Safety shutdown triggered because outlet water exceeded 203°F (95°C); check for heat exchanger scale, fan failure, or gas valve defect. |
17 | Venturi Blockage | Air intake or venturi throat passage obstructed; clean venturi assembly and perform button A/B diagnostic reset. |
19 | Electrical Grounding Fault | Immediate safety trip indicating an electrical short circuit in wiring harnesses, water flow control, or 12V/24V DC components. |
21 | Data Transfer Error | PC board replaced without completing parameter programming or electronic data transfer. |
25 | Condensate Pump Error / Drain Clogged | External condensate overflow safety float switch tripped due to frozen, blocked, or failed condensate drain/pump. |
30 | Flammable Vapor Sensor | Flammable vapor detected or sensor circuit shorted on RH180 hybrid units. |
31 | Burner Thermocouple Fault | RH180 burner thermocouple voltage outside allowable range (less than 8 mV or above 30 mV). |
32 | Outgoing Water Temperature Thermistor | Temperature sensor on hot water outlet pipe is open, shorted, disconnected, or coated in scale. |
33 | Heat Exchanger Thermistor | Temperature thermistor seated directly in the primary heat exchanger body is defective or scaled. |
34 | Combustion Air Temperature Thermistor | Thermistor measuring intake air temperature inside fan housing is broken, open, or reading abnormal resistance. |
35 | Tank Temperature Sensor | Storage tank thermistor out of calibrated resistance specifications on RH180 hybrid units. |
38 | Exhaust Gas Temperature Sensor | Flue gas thermistor reading abnormal exhaust temperatures; inspect venting lengths, DIP settings, or sensor resistance. |
41 | Freeze Protection Sensor | Outside air ambient temperature thermistor on outdoor models is damaged, unplugged, or defective. |
51 | Inlet Water Temperature Thermistor | Cold water inlet thermistor reading open or short circuit; check wiring and sensor resistance. |
52 | Gas Valve Solenoid / Modulating Valve (POV) | Modulating proportional solenoid valve electrical abnormality; inspect wiring, coil resistance, or replace gas valve. |
54 | High Exhaust Gas Temperature | Exhaust gas temperature exceeded 163°F for over 120 seconds; clear heat exchanger fins and flush mineral scale. |
57 | Burner Overheat Bi-Metal Switch | High-limit safety bi-metal switch on rear of burner opened; verify gas supply type, manifold pressure, and elevations. |
58 | Secondary Heat Exchanger Sensor | Overheat bi-metal switch opened on secondary condensing heat exchanger; mandatory system flush required. |
61 | Combustion Fan Motor | Combustion blower fan wheel stuck with debris, damaged wiring harness, or failed blower motor windings. |
63 | Recirculation Low Flow | Flow rate through the domestic hot water recirculation loop is too low; check bypass plug, dirty inlet filters, or loop airlocks. |
65 | Water Flow Control Device | Motorized water flow servo valve failed to close during automated bath-fill function. |
70 | PC Board Fault | Internal electronic processing failure on main circuit board; verify parameters or replace board. |
71 | Gas Solenoid Valve Fault | Gas solenoid safety valves (SV0, SV1, SV2, SV3) open, shorted, or moisture present in combustion air sensing tube. |
72 | Flame Rod Circuit Fault | Flame sensor rod detecting flame before ignition or reading under 1 micro-amp during normal combustion. |
73 | Burner Thermocouple Fault | Thermocouple on Non-SENSEI models failed or high/low manifold pressures require recalibration. |
79 | Water Leakage Detected | Moisture sensor on bottom pan of water heater casing detected liquid pooling from internal leaks or loose fittings. |
FE | Flammable Vapors Detected | RH180 combustible gas detector tripped; immediately shut off power, ventilate room, and isolate gas lines. |
FF | Maintenance Performed History | Informational log entry entered by service technician indicating maintenance was completed. |
SE | Cascade Diagnostic Display | Commercial SENSEI™ multi-unit cascade link alert; indicates a secondary linked unit has registered a fault. |
SS (55) | Service Soon Alert | Time-based maintenance reminder (0.5 to 2 years) programmed during setup; flush heat exchanger to clear. |
LC / LC0–LC9 | Scale Build-Up in Heat Exchanger | Severe mineral lime scale detected inside heat exchanger piping; requires immediate descaling flush. |
No Code | Flow Issues or Tripped GFCI Breaker | Clean cold water inlet screen, ensure minimum activation flow (0.4 GPM) is met, or inspect pump shaft O-ring on RUR units. |
Rinnai Tankless Water Heater Models Covered
The error codes and diagnostic procedures documented above apply directly to the following Rinnai residential,commercial, and hybrid models:
Non-SENSEI™ Series
Series Category | Model Name | Series Identification / Part Number |
Value VC | V53e | REU-VAM1620W-US |
Value VC | V53De | REU-AM1620WD-US |
Value VC | V65i | REU-VC2025FFU-US |
Value VC | V65e | REU-VC2025W-US |
Value VC | V75i | REU-VC2528FFU-US |
Value VC | V75e | REU-VC2528W-US |
Value VC | V94i | REU-VC2837FFU-US |
Value VC | V94Xi | REU-VC2737FFU-US |
Value VC | V94e | REU-VC2837W-US |
Luxury VC | RL75i / RL75i(A) | REU-VC2528FFUD-US / REU-VC2528FFUD-US(A) |
Luxury VC | RL75e / RL75e(A) | REU-VC2528WD-US / REU-VC2528WD-US(A) |
Luxury VC | RL94i / RLX94i | REU-VC2837FFUD-US / REU-VC2737FFUD-US |
Luxury VC | RL94e | REU-VC2837WD-US |
KCM | RUCS65i / RUCS75i | REU-KCM2025FFU-US / REU-KCM2528FFU-US |
KCM | RUS65e / RUS75e | REU-KCM2025W-US / REU-KCM2528W-US |
KBD | RUC80i / RUC90i / RUC98i | REU-KBD2530FFUD-US / REU-KBD2934FFUD-US / REU-KBD3237FFUD-US |
KB | RU80i / RU80e | REU-KB2530FFUD-US / REU-KB2530WD-US |
KB | RU90e / RU98i / RU98e | REU-KBD2934WD-US / REU-KB3237FFUD-US / REU-KB3237WD-US |
KBP | RUR98i / RUR98e | REU-KBP3237FFUD-US / REU-KBP3237WD-US |
Commercial | C199i / C199e | REU-KBD3237FFUDC-US / REU-KB3237WDC-US |
HTT (Hybrid) | RH180 | REU-VA1320WF-US |
SENSEI™ Series
Series Category | Model Name | Series Identification / Part Number |
SENSEI™ Residential | RU199i / RU199e | REU-N3237FF-US / REU-N3237W-US |
SENSEI™ Residential | RU180i / RU180e | REU-N2934FF-US / REU-N2934W-US |
SENSEI™ Residential | RU160i / RU160e | REU-N2530FF-US / REU-N2530W-US |
SENSEI™ Residential | RU130i / RU130e | REU-N2024FF-US / REU-N2024W-US |
SENSEI™ Residential w/ Pump | RUR199i / RUR199e | REU-NP3237FF-US / REU-NP3237W-US |
SENSEI™ Residential w/ Pump | RUR160i / RUR160e | REU-NP2530FF-US / REU-NP2530W-US |
SENSEI™ Commercial | CU199i / CU199e | REU-N3237FFC-US / REU-N3237WC-US |
SENSEI™ Commercial | CU160i / CU160e | REU-N2530FFC-US / REU-N2530WC-US |
How to Check Past Fault History on Your Controller
If your water heater stopped working earlier but the controller screen is currently blank or only displaying target water temperature, you can check the last 9 recorded fault codes stored in memory:
Turn the water heater off by pressing the On/Off button.
Press and hold the On/Off button for 2 seconds, then press the ▲ (Up) button at the same time.
The display will sequentially flash through the last 9 maintenance codes in order of occurrence.
To return to normal operating mode, press and hold the On/Off button for 2 seconds and tap ▲ (Up)simultaneously, then power the unit back on.
Frequently Asked Questions
Why does my Rinnai flash an error code only during showers?
This usually stems from either a fluctuating gas supply under continuous load (Code 11 or 12) or a low-flow cold water sandwich. If you use low-flow showerheads (under 1.5 GPM), the flow rate can dip below the minimum water flow required to keep the burner firing, causing the unit to cycle off.
Can I run my water heater when it displays Code LC?
Yes, temporarily. Code LC is the only error code that permits ongoing operation. It alerts you that scale has reached an unsafe threshold. Pressing the On/Off button 5 times will allow an additional 70 hours of hot water before the unit locks out again to prevent the heat exchanger from melting or cracking.
Can I clean Rinnai flame rods myself?
If you are comfortable isolating electrical power and gas lines, you can remove the flame sensor rod and polish off carbon deposits with fine 0000 steel wool or an abrasive pad. However, if the ceramic insulator is cracked or the gasket tears during removal, you must replace the component to prevent fuel gas leaks.
Expert Rinnai Tankless Service in Seneca, SC
While basic troubleshooting can help you identify what went wrong, opening the cabinet to test gas pressures, fan voltage, and combustion circuits involves live electrical testing and fuel gas safety procedures. Incomplete repairs can risk combustion leaks or void your manufacturer warranty.
If your Rinnai tankless system is locked out on a stubborn error code, contact All Hot Water LLC. Located right here in Seneca, SC, we serve Lake Keowee, Clemson, Anderson, and all of Oconee County with expert tankless water heater repair, precision descaling flushes, and seamless replacements.
Visit us online at www.allhotwaterllc.com or contact our local service team today to schedule fast, certified diagnostic service.
Need all the details? You can view and download the complete Official Rinnai Troubleshooting Tankless Water Heater Diagnostic Codes Guide for complete fault code information.
Source & Trademark Disclaimer:
Diagnostic code data, model numbers, and technical procedures are referenced from the official documentation provided by Rinnai America Corporation. "Rinnai" and "SENSEI" are registered trademarks of Rinnai America Corporation. All Hot Water LLC is an independent water heater repair and installation service provider and is not directly affiliated with or endorsed by Rinnai America Corporation. For full product manuals and warranty terms, visit www.rinnai.us.
Comments