Noritz Code 12: Flame Loss
On this page (6 sections)
The Short Answer: On Noritz gas tankless heaters, code 12 is “Flame Loss”: the burner lit, then the flame went out or the unit stopped detecting it. Common causes are a gas supply that can’t keep up when the burner fires hard, a propane tank running low, a venting or wind problem, and a dirty flame rod. Check your gas supply and vent, reset once, and call a technician if it returns.
Code 12 versus 11 and 10
Noritz training material lists 11 as ignition failure (the burner never proved flame) and 12 as flame loss (opens in a new tab) (it lit, then lost it). That difference matters. With 12, the ignition system worked at least once, so the question is why the flame couldn’t be sustained.
If your display shows 11, see Noritz code 11. Code 10 relates to combustion and venting.
Common causes of code 12
| Pattern | Likely cause | Who handles it |
|---|---|---|
| 12 mainly when several fixtures run, or when the furnace is also on | Gas line too small or gas pressure dropping under load | Gas technician |
| 12 on a propane system, recently or suddenly | Tank low, regulator problem, or freezing regulator in cold weather | Owner checks tank; supplier or technician for regulator |
| 12 on windy days, outdoor unit | Wind affecting the flame or exhaust | Technician may recommend a vent or wind accessory |
| 12 with exhaust smell or soot | Venting problem or poor combustion | Shut down; technician |
| 12 intermittently, gas supply fine | Dirty or worn flame rod, or a combustion fan issue | Technician |
| 12 since a new installation or gas work | Undersized gas line, air in the line, or wrong gas type | Installer |
Noritz’s EZ series training (opens in a new tab) specifically names an undersized gas line as a cause of 11, 12, and combustion codes. A large tankless burner needs much more gas than a tank heater, and a line that is fine at low fire may not keep up at full fire.
What you can check safely
- Write down the code and when it happened: during a single shower, when several taps ran, or in cold or windy weather.
- Confirm the gas valve to the heater is fully open and other gas appliances are working.
- On propane, check the tank level. Low tanks and cold weather together are a common cause.
- Look at the outdoor vent or the outdoor unit for snow, ice, nests, or debris.
- Turn the unit off and on with the remote controller (or the power switch) once. If 12 returns, leave it off and call for service.
Repeated resets on a flame fault can send unburned gas through the burner, so don’t keep cycling it.
What the technician will check
A Noritz-qualified technician will measure gas pressure at the heater both at rest and with the burner at full fire, which is the usual way to find an undersized or overloaded gas line. They also inspect and clean the flame rod, check the combustion fan and the vent run, and confirm the unit is set for the correct gas type. On outdoor units they look at how the heater is exposed to wind.
Repair or replace
Most code 12 causes are fixable: a gas line upgrade or regulator, a cleaned or replaced flame rod, venting corrections, or a fan. Replacement is usually only on the table when an older unit also has a failing heat exchanger or repeated control problems.
Related: tankless water heater not working after rain and Noritz tankless water heater not working.
Frequently Asked Questions
Q: Why does code 12 only appear when two showers run? A: That points strongly to the gas supply. At higher demand the burner fires harder and needs more gas. If the line or meter can’t supply it, the flame weakens and the unit records a flame loss.
Q: Can I clean the flame rod myself? A: The flame rod is inside the sealed combustion section behind the front cover. Cleaning or replacing it is a technician job.
Q: Is code 12 dangerous? A: The code itself means the safety system shut the burner off. Treat it as a problem to fix, and if you also smell gas or exhaust, leave and call for help.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- Noritz: Residential Level 2 Maintenance and Troubleshooting (training) (opens in a new tab)Noritz residential gas tankless training material listing codes 11 (ignition failure) and 12 (flame loss); models not individually listed.
- Noritz: EZ series training (EZ111DV/EZTR75, EZ98DV/EZTR50) (opens in a new tab)Noritz EZ tankless models named in the document; links undersized gas lines to codes 10/90, 11 and 12.
- Noritz: product support and technical literature (opens in a new tab)Find the specific model’s owner guide and code definitions.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
Editorial standards and corrections · Prepare a useful service request