DIY Error Codes

Rinnai Tankless water heater Code 12

The burner lit and then the flame went out.

Make sure the gas is on and a propane tank is not empty. Anything further is gas-system work for a pro.

Start the fix →When to call a pro ↓
Full answer & models

Rinnai code 12 means: Flame Failure. Make sure the gas is on and a propane tank is not empty. Anything further is gas-system work for a pro.

Applies to: SENSEI™ SeriesNon-SENSEI™ Series
Also searched as: Rinnai code 12, Rinnai error 12, Rinnai error code 12

If you smell gas, leave the building and call your gas supplier from a neighbor's phone. Do not touch switches or use any phone inside.
Why
If you smell gas: do not try to light any appliance, do not touch any electrical switch, and do not use any phone in your building. Leave and call your gas supplier from a neighbor's phone; if you cannot reach them, call the fire department. Rinnai states that only trained and qualified professionals may follow its diagnostic-code service instructions, and that power, gas and water must be turned off before servicing. Never operate the heater with any vent pipe disconnected. Do not adjust the internal gas valve. Burn hazard (Rinnai): hot exhaust and vent may cause serious burns; keep small children and animals away, and hot water outlet pipes can be hot to touch.

What 12 means

The burner lit and then the flame went out.

More detail
Rinnai's diagnostic-code guide (page 18) titles code 12 "Flame Failure". Rinnai's guide is written for trained, qualified professionals, so this page lists only the owner-level checks and tells you when to stop.

5-minute checks

Fix it step by step

Step 1 of 2

  1. Check that the gas is on

    • 2 min
    • None
    • DIY

    Safety: If you smell gas, leave the building and call your gas supplier from a neighbor's phone. Do not touch switches or use any phone inside.

    At the heater, gas meter or propane tank.

    More detail

    Check that the gas is on.

    Rinnai's guide, code 12: ensure the gas is turned on at the water heater, gas meter or propane tank, and that a propane tank has gas in it.

    Did the code clear?

  2. Call a licensed pro

    • Decision
    • None
    • Pro decision

    Stop here and book a qualified technician.

    More detail

    Call a licensed pro.

    Rinnai prefaces its code 12 steps with a warning that you must be qualified to service gas systems (inlet pressure, flame rod, gas system sizing).

    Still showing 12?Need a pro → call a pro

Code cleared. Nice work.

Watch the display for a day to make sure it stays clear.

Back to top

Fixed after any step? Watch the display for a day to make sure it stays clear. Still 12 after step 2? call a pro.

Call a pro if…

  • Gas is on and code 12 returns.
  • You smell gas.

FAQ

What does Rinnai code 12 mean?

Flame failure, per Rinnai's diagnostic guide.

Source: Rinnai, Troubleshooting Tankless Water Heater Diagnostic Codes (100000652), page 18. Written by the DIY Error Codes team. Updated 2026-10-16. DIY Error Codes is independent and not affiliated with or endorsed by Rinnai.