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Rinnai code 12 (no flame): what to check

By How House Works EditorialBased on Rinnai manualsChecked against sources Updated

Rinnai display

12

“No Flame”

RU/RUR/RSC, RX, RE/REP, V, RL/VC · SENSEI RU Installation and Operation Manual, p. 73; SENSEI RUR Installation and Operation Manual, p. 72; SENSEI RSC Installation and Operation Manual, p. 72; SENSEI RX/CX Tech Sheet, p. 1; RE Series Installation and Operation Manual, p. 50; REP Series Installation and Operation Manual, p. 49; Value Series Installation and Operation Manual, p. 34; V53De Installation and Operation Manual, p. 28; VC Series Installation and Operation Manual, p. 37; Troubleshooting Tankless Water Heater Diagnostic Codes, p. 20–21
Owner checks, then technician

What it means

Rinnai’s troubleshooting guide titles code 12 “Flame Failure” p. 20. The owner checks start the same way as for code 11, with the gas supply and the propane tank RU manual, p. 73. The RE, REP, Value, V53De and VC tables add a look at the flue outlet RE manual, p. 50; Value manual, p. 34.

The guide’s list for the technician covers inlet gas pressure and gas pipe sizing, the flame rod and spark electrode, grounding of the electrical circuit, and debris or insects in the fan. It also names venting faults that let combustion gases recirculate, which it says may cause incomplete combustion and code 12 pp. 20–21. If code 12 shows immediately after water starts to flow, the guide points to an electrical short in one of the heater’s DC components p. 21.

Check these first

Rinnai’s tables warn that consumers should never attempt any action they are not qualified to perform RU manual, p. 73; Value manual, p. 34. The V53De manual adds: call a licensed professional for any remedy that involves gas or electricity, or if you have any doubt about doing it yourself V53De manual, p. 28. If you smell gas, the Value and V53De manuals put one step before those in the box above: leave the premises Value manual, p. 28; V53De manual, p. 22.

  1. Check that the gas is turned on at the water heater, the gas meter, or the cylinder RU manual, p. 73; Value manual, p. 34. Turn the manual gas valve by hand only, never with tools RU manual, p. 8. If the valve at the heater was closed, reopen it only as the operating instructions describe, including the five-minute wait with the valve off and the check for a gas smell near the floor RU manual, p. 68; Value manual, p. 29.
  2. If the heater runs on propane, make sure there is gas in the tank RU manual, p. 73; Value manual, p. 34.
  3. Outside, check the flue outlet for obstructions Value manual, p. 34; RE manual, p. 50. Keep the area around the flue terminal free of snow and ice RU manual, p. 77. If the vent is blocked and you cannot easily clear it, contact a trained and qualified professional RU manual, p. 76.
  4. If the heater still does not run, turn off the gas to the appliance as the operating instructions describe, then call a service technician or the gas supplier RU manual, p. 68; Value manual, p. 29.

When to call a licensed technician

The Value, V53De and VC tables mark these remedies “licensed professional only” Value manual, p. 34; V53De manual, p. 28; VC manual, p. 37:

  • Gas line, meter and regulator sizing, gas type and pressure, and bleeding air from the gas lines. Inlet pressure ranges differ by series; the Rinnai code 11 page lists them with sources and conditions.
  • The condensation collar. The Value and VC tables also list the venting material and vent length Value manual, p. 34; VC manual, p. 37; the V53De table does not p. 28.
  • DIP switch settings.
  • Power supply connections, voltage and voltage drops, wiring harnesses, and DC shorts at components.
  • The flame rod wire, carbon build-up on the flame rod, the gas solenoid valves, and condensation or debris on the burner surface.

The troubleshooting guide stresses a properly grounded circuit and, if there is any doubt, sends the circuit to a licensed electrician p. 21.

Notes for different models

The RU, RUR, RSC and RX tables list five remedies for code 12: gas on, gas in the propane tank, the flame rod wire, gas type and inlet pressure, and bleeding air from the gas lines RU manual, p. 73; SENSEI RX/CX Tech Sheet, p. 1. The flue outlet check appears only in the RE, REP, Value, V53De and VC tables RE manual, p. 50; REP manual, p. 49; V53De manual, p. 28; VC manual, p. 37.

Related Rinnai codes

  • 11 “No Ignition (Heater Not Turning On)”
  • 72 “Flame Rod”
  • 19 “Electrical Grounding”

All Rinnai codes

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Sources

  1. Rinnai America Corporation. Troubleshooting Tankless Water Heater Diagnostic Codes. 100000652(03), 5/2024; for trained and qualified professionals. Accessed Oct 12, 2026.
  2. Rinnai America Corporation. SENSEI RU Installation and Operation Manual. 100000467(07), 1/2021; cover title: Tankless Water Heater (Residential) Installation and Operation Manual; listed on rinnai.us as N Series Residential Condensing Installation and Operation Manual. Accessed Oct 12, 2026.
  3. Rinnai America Corporation. SENSEI RUR Installation and Operation Manual. 100000508(07), 1/2021; cover title: Tankless Water Heater (With Pump) Installation and Operation Manual. Accessed Oct 12, 2026.
  4. Rinnai America Corporation. SENSEI RSC Installation and Operation Manual. 100000773(01), 1/2023. Accessed Oct 12, 2026.
  5. Rinnai America Corporation. SENSEI RX/CX Tech Sheet. 100000849, U362-0875(00); no printed date or page numbers (p. 1 is the PDF page). Accessed Oct 12, 2026.
  6. Rinnai America Corporation. RE Series Installation and Operation Manual. 100000722(03), 6/2022; cover title: Tankless Water Heater Installation and Operation Manual. Accessed Oct 12, 2026.
  7. Rinnai America Corporation. REP Series Installation and Operation Manual. 100000726(03), 3/2022; cover title: Tankless Water Heater (With Pump) Installation and Operation Manual. Accessed Oct 12, 2026.
  8. Rinnai America Corporation. Value Series Installation and Operation Manual. 100000258(10), 4/2021; cover title: Direct Vent Tankless Water Heater Installation and Operation Manual. Accessed Oct 12, 2026.
  9. Rinnai America Corporation. V53De Installation and Operation Manual. 100000561(05) (from the file name; no printed revision or date). Accessed Oct 12, 2026.
  10. Rinnai America Corporation. VC Series Installation and Operation Manual. 100000244(12), 8/2019; cover title: Direct Vent Tankless Water Heater Installation and Operation Manual. Accessed Oct 12, 2026.