Noritz Tankless Water Heater Error Code 12: Meaning and Fix

Applies to: Noritz tankless water heaters (residential and Pro Series premix models; each Noritz help article notes which models it covers).

How 12 appears on a Noritz tankless water heater display.

Reading the tankless water heater display

A tankless water heater shows its fault as a number or letter code on the unit display or on the wired remote controller, and some models keep a short history of past codes. Write the code down exactly as shown before you reset the unit, and check the rating plate for the model number, because the same number can mean different things between series.

Noritz makes gas tankless water heaters that show a numeric error code on the display or the remote. Its help center documents each code, and the steps differ between residential and Pro Series premix models. Check the model label on your unit before using any chart.

What causes 12

Dirty flame rod
Intake pulling in exhaust on direct vent units, or damaged exhaust O-rings on DVC models
Gas supply too low to keep the flame lit

How to fix it

If you smell gas, leave the building and call your gas utility from outside; do not touch switches or the unit. Switch the water heater off and let it cool before you touch any internal part, and call a licensed plumber or water heater technician if you are not sure.

The code meaning comes from the manufacturer document listed under Sources. The causes and steps below are general troubleshooting guidance, not the manufacturer's service procedure.

Switch the water heater off and let it cool before you touch anything inside it. If you smell gas, leave the building and call your gas utility from outside.
Clean the flame rod.
Check the venting, especially on direct vent units where the intake may pull in exhaust.
On DVC models, inspect the 3 inch exhaust O-rings for damage or absence.
Leave gas pressure testing to a professional.
If the code returns after these checks, call a licensed plumber or water heater technician and give them the code and the model number from the rating plate.

Questions

What does Noritz tankless error code 12 mean?

Code 12 on a Noritz tankless water heater means a flame is detected and then goes out during operation, which points to a weak flame.

Can I reset the water heater myself?

Turning the unit off and back on, or unplugging it for about 30 seconds, clears some codes. If the same code comes back, the fault is still there and the unit will shut down again. Do not bypass a safety device to keep it running.

When should I call a technician?

Call a licensed plumber or water heater technician for anything involving gas, venting, the heat exchanger, a thermal fuse or the circuit board, or when the code keeps returning after the simple checks.

Other brands with code 12

The same code can mean something different on another maker's appliance. Check the brand before you act.

Bryant furnaceBlower on after power up Carrier furnaceBlower on after power up Chamberlain garage door openerSafety sensor wire shorted or reversed Craftsman garage door openerSafety sensor wire shorted or reversed LiftMaster garage door openerSafety sensor wire shorted or reversed Payne furnaceBlower on after power up Rheem tankless water heaterGas service interrupted or LP gas low Rinnai tankless water heaterFlame failure

Other Noritz tankless water heater codes

06Recirculation flow too low (NRCR)10Combustion warning (can lead to code 90)11Ignition failure 14Heat exchanger overheat (thermal fuse)16Outlet water temperature too high 20High limit switch tripped

Sources

Part numbers are OEM references; confirm fit by your model number before ordering. Meanings compiled from manufacturer and parts-retailer documentation; see sources below. Unplug the appliance before opening it.