HeatingCodes

Rinnai tankless water heater diagnostic codes

By Jason Dearmin · Last reviewed November 14, 2026

Rinnai tankless water heaters show a two-digit diagnostic code on the display or remote when they shut down for a fault. Rinnai publishes one troubleshooting document that walks through each code, and the first steps are usually the gas supply and the vent.

What this table coversTitles from the table of contents of Rinnai's "Troubleshooting Tankless Water Heater Diagnostic Codes" document, which covers SENSEI, SENSEI RX/CX and non-SENSEI series. A code only applies to the models listed in that section of the document.

How to read the display

Write down the code and your model number before you reset anything. Some codes only apply to certain series, so the model matters.

Rinnai's own document warns that several of the deeper steps (gas pressure, gas valve, flame rod, vent disassembly) must be done by someone qualified to service gas systems.

Rinnai code table

CodeMeaningWhat the document says
03 Power interruption during bath fill
05 Bypass flow control device
07 Circulation flow rate below 2.1 GPM
10 Air supply, exhaust blockage or condensate trap is full Full explanation
11 No ignition Full explanation
12 Flame failure Full explanation
13 Combustion (RH180 hybrid tank-tankless only)
14 Thermal fuse or overheat sensor (ODS)
15 Venturi control
16 High outgoing water temperature
17 Venturi blockage
18 Gas valve adjustment limit
19 Electrical grounding
21 Data transfer error
22 Gas valve adjustment
25 Condensate pump error or drain is clogged (accessory pump)
30 Flammable vapor sensor
31 Burner thermocouple
32 Outgoing water temperature thermistor fault
33 Heat exchanger thermistor
34 Combustion air temperature thermistor (non-SENSEI series)
35 Tank temperature sensor
38 Exhaust gas temperature sensor
41 Freeze protection sensor (external water heaters)
51 Inlet water temperature thermistor
52 Gas valve
54 High exhaust gas temperature
57 Burner overheat bi-metal switch
58 Secondary heat exchanger sensor
61 Combustion fan motor
63 Recirculation low flow
65 Water flow control device
66 Bypass flow servo
70 PC board fault
71 Gas solenoid valve
72 Flame rod fault
73 Burner thermocouple fault
79 Water leakage detected
FE Flammable vapors detected
FF Maintenance has been performed

Source: Rinnai TWH diagnostic code document, table of contents. We list titles only for codes where we have not summarized the troubleshooting steps.

Detailed explanations

SafetyThese tables describe what the manufacturer documents say. Gas, combustion, refrigerant and line-voltage repairs are for licensed professionals. If you smell gas, leave the building and call your gas utility or 911. Safety disclaimer.

Sources