On a Noritz tankless water heater, code 11 means ignition failure, 12 means the flame was lost, and 90 and 99 are combustion abnormalities. All four point first to gas supply, then to the flue and air path and the flame rod. Turn the heater off and on to reset. If a code returns, stop and call a technician.
What do Noritz codes 11, 12, 90 and 99 mean?
Here is what Noritz says about each, drawn from its own technical article and its service manual.
- Code 11, ignition failure. Noritz explains that three things are needed to ignite a tankless heater: air, spark and gas. Code 11 means one or more of them is missing. Its article lists no propane in the storage tank, a disruption in the gas supply line, airflow problems, or debris on the ignition plug. The service manual's checkpoints are the gas supply piping and pressure, the igniter spark, the gas solenoid valves, the flame rod and the ground.
- Code 12, flame lost. The service manual calls it a flame rod that does not detect flame. Noritz's article describes it as the flame igniting and then not staying lit. Its checkpoints include an accidental extinction of the flame, abnormal combustion, the gas solenoid valves, the flame rod and the ground, especially on the circuit board.
- Code 90, combustion abnormality. Noritz says the heater makes three attempts to reach the set temperature, and shows 90 after the third failed attempt. The article gives two possible causes: insufficient gas pressure, or an internal problem where the air intake, the exhaust and the general cleanliness of the unit need to be inspected. Noritz's fix for the internal cause is cleaning the unit with compressed air to remove dirt and lint. The service manual lists two versions of 90: a warning indication, and one where the unit shuts off.
- Code 99, combustion abnormality. The service manual lists it as a combustion abnormality where the unit shuts off. The checkpoints are to check for abnormal combustion and to check the flue for blockage or obstruction.
Noritz's own article lists gas pressure as a cause of codes 11, 12 and 90, and names a digital gas manometer as the tool that shows it accurately.
How do I reset a Noritz tankless heater?
The service manual gives a simple rule. If the flame rod does not detect a flame, or if the high limit switch trips, the gas valves close, the flame goes out, and a code flashes on the remote controller. To reset, turn the power off with the Operation Button on the remote controller, then press it again to turn the unit back on.
That is enough for the ordinary case. The manual adds two important limits:
- Some codes need power disconnected. The service manual's table lists codes that need the power to be disconnected and reconnected to reset. Codes 90 in its shut-off form, 99, 10 and 20 are on that list, along with 65, 73, 91 and 94. If pressing the Operation Button does not clear it, cutting power at the plug or breaker and restoring it is the reset that manual describes.
- Some codes will not reset at all. The manual says if the problem needs service, such as a triggered thermal fuse, the gas valves stay closed, and resetting will not remove the code. The unit has to be serviced before it will work again.
For code 11 on a new installation, Noritz's installation manual says something specific. During the trial operation, if an 11 appears, turn the unit off and on, then open a hot water fixture again. Air in a new gas line can take a few tries to clear.
If a code clears and stays away, you are done. If it comes back the same day, stop resetting. Each cycle repeats the same failed attempt.
### What can I check safely?
Start with the gas smell rule. If you smell gas, do not touch a switch or use a phone inside, do not try to light anything, and leave. From a safe spot outside, call 911, and call Southwest Gas on 877-860-6020 if you are one of its Phoenix area customers.
If there is no smell, these are homeowner checks:
- 1Fuel. On propane, make sure the tank has fuel. Noritz names low propane as a cause of code 11.
- 2The gas valve. Confirm the gas shutoff to the heater is fully open.
- 3Other gas appliances. If the range or dryer is also weak or out, the trouble is in the supply, not the heater.
- 4The vent terminal. Look outside for anything blocking the exhaust or the air intake, such as leaves, a nest or something leaned against the wall. Never touch a hot exhaust.
- 5The timing. Note whether the code appears in cold weather, when several gas appliances run at once, or after new work on the house. Noritz's article ties poor supply pressure to periods when multiple heating appliances run together, such as winter.
Do not open the cabinet. The igniter and flame rod sit next to gas and high voltage.
Why do these codes come back?
Noritz's article and manuals point at the same short list.
Gas pressure. Noritz says an undersized gas supply prevents the heater from reaching maximum performance, and that weak supply pressure leads to a weak flame that cannot meet demand. The installation manual for the NRC83 and NRC98 outdoor models gives the supply pressures that must be available even at maximum demand: 4 to 10.5 inches of water column on natural gas, and 8 to 14 on LP gas. It says to size the gas line for the total demand of the building and the length from the meter. A heater added to an old gas line, or a line shared with a range, dryer and barbecue, can fall short.
The air path. Codes 10, 90 and 99 all lead to the flue and air inlet. The manual says to check both for blockage or obstruction. Noritz's fix for a dirty interior is compressed air to clear the built-up dirt and lint.
The flame rod and ground. Codes 11 and 12 both list the flame rod and the ground in the manual's checkpoints. A dirty or loose flame rod, or a weak ground at the circuit board, can mimic a fuel problem.
No code at all. Noritz also warns that a heater will not show an error if it does not sense demand. It says its units meet a hot water demand as small as 0.5 gallons per minute, so a trickle from a fixture may not fire the heater and no code will appear.
### What will a technician do?
A technician measures the inlet gas pressure with a manometer while the heater fires, and compares it to the supply pressure the manual requires. They check the gas type against the rating plate, test the igniter spark and the solenoid valves, inspect the flame rod and the ground, and check the flue and air inlet for blockage. If the interior is dirty, they clean it out. For codes that the manual says will not reset, they test the thermal fuse and safety circuit.
One caution about this page. The code tables above come from Noritz's manuals for the NRC83, NRC98 and related series. Newer Noritz models, and condensing or commercial units, can label codes differently. Your rating plate gives the model, and the owner's manual for that model rules over any chart, including this one.
When should I call a plumber?
Call when a code returns after one reset, when a reset will not clear it, when several gas appliances are weak at once, or when the heater has stopped making hot water. Noritz's manuals treat gas pressure measurement and the interior of the cabinet as service work. HQ Plumbing and Air is licensed and insured, and handles emergency calls 24/7. The estimate is free and the price is quoted upfront before work starts.
If your heater is a different brand, see our pages on Rinnai error code 11, Rinnai error code 12 and Navien error code E003, which cover the same ignition and flame problems with different numbers. Because Phoenix has hard water, our page on how often to descale a tankless water heater is a good next read. And when a heater is old and the codes keep stacking up, our page on whether to repair or replace a water heater can help.