Noritz 12

Noritz error code 12: flame loss, causes and fixes

By USA Expert Plumbing Editorial Team. Updated September 27, 2026. 1 min read.

Short answer

Code 12 means the Noritz detected a flame but then lost it. Like code 11, it is usually caused by a problem with the gas supply or airflow.

Where code 11 means the burner never lit, code 12 means it lit and then the flame was lost. Noritz describes it as a flame loss.

What to check

Note whether code 12 appears when other gas appliances are running; that points to gas pressure.
Check the vent terminal outside for blockage, snow or ice.
Confirm the gas valve is fully open and the propane tank, if used, has gas.
Reset the unit at the remote.

If code 12 returns, a licensed contractor will test gas pressure with everything running and check the flame sensing parts and venting.

What is the difference between Noritz code 11 and 12?

Code 11 means the burner did not light at all. Code 12 means it lit and then lost the flame.

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Code	Meaning
10	Combustion abnormality (warning)
11	Ignition failure
12	Flame loss
13	Optional CO alarm device fault
14	Thermal fuse blown (severe overheat)
16	Outlet water temperature spiked too high
20	High limit switch tripped
29	Condensate drain problem (condensing models)
67	Air gas mixer (AGM) abnormality
71	Gas valve circuit abnormality
90	Combustion abnormality
92	Neutralizer near end of life (first warning)
93	Neutralizer at end of life