Noritz Code 12 indicates a flame failure during operation after a successful ignition. The most common fix is cleaning the flame rod of carbon buildup or checking for consistent gas pressure.
A Noritz Code 12 kills your shower mid-cycle because the unit loses its flame signal while it's running. Unlike ignition failures, this one means the system lit up just fine but couldn't hold it. I usually start looking at dirty flame sensors, venting obstructions, or gas pressure sagging under load. Ignore it and you'll get cold water every single time you try.
Phillips #2 screwdriver, Digital multimeter with microamp setting
What Does the 12 Code Mean?
Dealing with a code 12 is often a game of timing. If your Noritz runs fine for a few minutes and then drops out, you're probably looking at a sensing issue or a pressure sag. It's rarely a total parts failure. Most of the time, a simple cleaning or a quick adjustment to your gas supply fixes the problem for good. I've seen this code pop up on units that are only two years old, so age isn't always the factor.
Most Likely Causes
Based on aggregated repair data, here is the probability breakdown for this error code:
Gas pressure dropping during high-demand periods40%
Worn or contaminated flame rod losing signal mid-cycle24%
Vent restriction reducing available combustion air22%
Water flow rate dropping below minimum threshold during use14%
Symptoms You May Notice
Code 12 shows up on the remote display after 30 to 90 seconds of normal hot water use, then the water goes cold.
Water temperature feels fine for the first minute of your shower, then suddenly drops to cold and you can hear the unit shut off.
The unit restarts okay if you turn the tap off and back on, but drops out again after roughly the same amount of time.
Code 12 only pops up when two or more fixtures are running hot at the same time, like the shower and the kitchen sink going simultaneously.
You can actually hear the burner ignite and then click off with the error, even though you never touched the hot water tap.
Can you reset a Noritz waterheater to clear the 12 code?
Hit the power button on your remote controller to turn it off, wait about 5 seconds, then turn it back on. If you don't have a remote, unplug the unit for 30 seconds. That's all there is to it. But here's the thing: resetting just clears the display. If the flame rod's still dirty or your gas pressure's still sagging, code 12 will be back the next time you run hot water. Fix the root cause first, then reset.
Tools Required for Diagnosis
Phillips #2 screwdriverDigital multimeter with microamp settingManometer for gas pressure testing, 0-15 inches WC range000 grade fine steel wool5-gallon bucket and stopwatch for flow rate testing
Diagnostic Checklist
Follow these steps in order. We start with the easiest external fixes before opening up the machine.
ComponentComponent Under Test
Expected Range1–10 µA
ConditionIf Open (OL) or infinite, replace component.
Replacement Parts
If your diagnostic testing proves the component has failed, you will need a replacement. We recommend OEM parts over aftermarket for water-handling components.
Part Name
OEM Number
Estimated Price
Flame Rod (Flame Sensor)100001706 · $12–$25
100001706
$12 – $25
Gas Pressure RegulatorN/A - utility-supplied or plumber-supplied · $30–$80
N/A - utility-supplied or plumber-supplied
$30 – $80
Frequently Asked Questions
What is the difference between Noritz Code 11 and Code 12?
Think of code 11 as a failure to start and code 12 as a failure to stay running. With an 11, the board never sees a flame at all. With a 12, the burner lit and actually worked for a bit, but then the flame signal disappeared mid-cycle. Both can involve the flame rod, but a 12 is way more likely to be a gas supply or venting issue. I've seen brand new flame rods cause a code 12 because the gas pressure was just barely too low. So don't assume it's always the sensor.
Why does Noritz Code 12 only happen in the morning?
Classic sign of an undersized gas system. In the morning your furnace is probably running and neighborhood demand is at its peak. That causes your incoming gas pressure to sag. If it drops too low, the Noritz can't hold a stable flame and code 12 fires. The fix might be a larger meter from the utility, a higher-capacity regulator, or running a bigger gas line to the heater. Either way, it's not the water heater's fault. Your utility can come out and test line pressure for free in most areas.
Can I clean the flame rod to fix Code 12?
Absolutely, and honestly it's the first thing I do on any code 12 call. Steel wool is the most-used tool in my bag for Noritz calls. Carbon and silica buildup on the rod is just inevitable over five to ten years of use. Cleaning it restores the electrical path the board needs to sense the flame. It's a zero-cost fix that solves about a third of the code 12 calls I run. Takes maybe 10 minutes total. Just use 000 grade, not the coarse stuff, and don't use sandpaper.
My Noritz runs for exactly 2 minutes then shows Code 12. What is that?
That consistent two-minute pattern is usually when the unit's internals reach peak operating temperature. Heat increases electrical resistance, and if a flame rod is borderline or a gas valve solenoid is starting to fatigue, the heat from normal operation will push it over the edge. I test the flame rod signal in microamps while the unit is running hot to confirm it. You're looking for a stable reading above 1 microamp. If it drops or flickers while the unit's warm, the rod needs replacing. A new flame rod usually runs $25 to $40 and takes about 20 minutes to swap out.
Does Noritz Code 12 indicate a gas leak?
Code 12 is actually a safety shutdown designed to prevent gas from flowing without a flame, so it's the unit doing its job correctly. But if you smell gas after a code 12 shutdown, that's a different issue entirely. It could mean the valve isn't seating cleanly after shutoff, or there's a leak somewhere inside the cabinet. If you catch any whiff of rotten eggs or sulfur, don't mess around. Shut off the gas at the main valve immediately and call your gas company. Don't try to troubleshoot a gas smell yourself.
How much does it cost to fix a Noritz Code 12?
If it's just the flame rod, you're looking at under $50 in parts and you can do it yourself. If it's a gas pressure issue, the fix might be free if your utility upgrades the meter, or it could run $200 to $800 if you need a new regulator or gas line work. A gas valve replacement is the expensive scenario, usually $150 to $300 in parts plus labor. But honestly, most code 12s I see get fixed with steel wool and 10 minutes of work. Start there before you spend any money.