Troubleshooting Tankless Water Heater Error Codes: Noritz

Owners of Noritz tankless water heaters may come across some of the error messages Noritz tankless water heaters can display, and they may or may not indicate a serious problem. An audible “beeping” alarm usually accompanies an error code. If you have no hot water, you may have exceeded your tankless water heater capacity or have at least one of the error codes below.

However, an error message is displayed for a reason and should never be overlooked or ignored, especially if you don’t know its implications.

In this article, you will find detailed information about Noritz tankless water heaters, their possible error messages, and what they mean.

No Error Code

There are a few instances where the unit doesn’t work correctly, but no error code is displayed. Usually, the most common problems in this case are:

• If the display doesn’t show the set temperature when the unit is powered, ensure that the correct power voltage and all the CB and remote controller readings are according to specifications. Check the unit’s fuse. Inspect the condition of the unit’s wiring.
• If the fan doesn’t work when the hot water valve is opened, this can be caused by a faulty water flow sensor or if the cold water thermistor detection is set too high or not working correctly.
• If the outlet water temperature is incorrect, ensure the cold water and hot water thermistors and heat exchanger are all working properly.

Error Code 5: Service warning

Noritz error code 5 means that it is time for the unit to be serviced by a licensed professional. Noritz code 05 is, thus, not an error code per se, but more of a reminder that your Noritz tankless water heater is due for servicing.

It is not recommended to ignore or reset this code as this can negatively affect your unit’s longevity.

Error Code 10: Combustion abnormality

Noritz error code 10 is a sign of a problem with the combustions of the unit. An error code 10 will show whether the output is uneven or the combustion doesn’t stop after powering the unit. Error code 10 can be caused by blockage or scale build-up on the burner. 

For example, grease, oil, or dirt accumulations on the burner can cause this error. The build-up continues to burn even after the unit has been completely switched off slowly.

If you have a recirculation loop, ensure that you have a 10-degree water differential.

You can reset this error code by turning the unit off and on again.

Error Code 11: Ignition Failure

Noritz error code 11 indicates a problem with the ignition of the tankless water heater. Noritz error code 11 can be caused by low gas supply or airflow, bad wiring, or scale build-up on the igniter. Maintenance and flushing service will usually correct the problem.

Ensure that you are using the right type of gas, that the gas flow is working, and the pressure is within the recommended ranges.

Check the condition of the ignition plug, clean it, and ensure it is installed correctly.

Make sure the unit is grounded and there are no short circuits.

If nothing helps, have a trained technician inspect the unit.

We have a how-to guide for tankless water heater maintenance. In Easy Maintenance Tips for Tankless Water Heaters w/Photos will outline how to perform tankless water heater flushing and other maintenance.

Error Code 12: Flame rod does not detect flame; flame loss during operation

Noritz error codes 12 means that the flame is not strong enough to heat the water properly. Noritz error code 12 can be caused by low gas supply and airflow. Scale build-up on the igniter plug or loosely fitted igniter can also cause this problem.

An error code 12 will be displayed on the remote controller on some models, while on the unit’s display window, an error code 121 or 122 will display.

Check the gas pressure. Check the ignition plug for any scale build-ups if you are using the correct gas type, and the gas pressure is good. Make sure it is not loose. Check the grounding of the unit.

If the error continues to show, call a licensed contractor to assess the condition of the unit.

Error Code 14: Thermal fuse failure

Noritz error code 14 means there is a problem with the thermal fuse. Noritz error code 14 can be caused by poor water quality and restricted airflow. Replacing the thermal fuse will fix this error. In some instances, the heat exchanger may also have to be replaced and the whole unit to be cleaned.

Error Code 16: Abnormally high output water temperature

Noritz error code 16 means there is an increase in the outlet water temperature, and the unit is overheating, which is typically caused by scale build-up. Removing the scale build-up usually resolves this error code, and using a water softener will prevent this error code from appearing in the future.

You can remove the scale build-up by flushing the coil with a descaling solution. You can also use CLR or vinegar to flush the water heater for 60 to 90 minutes. For flushing instructions, see our tankless water heater maintenance guide.

This error code can also be caused by using the wrong type of gas, or the manifold pressure may need to be adjusted. In which case, it is recommended to have a licensed contractor assess the situation.

The error code 16 will appear on the remote controller on some models, while the display window on the unit can show error codes 161, 162, 163.

Error Code 20: High limit switch triggered

Noritz error code 20 means the high limit switch has been triggered. To fix the Noritz error code 20, you need to descale your tankless water heater, check the condition of the high limit switch, and replace it if necessary. To reset the error code, power off and on the unit.

Error Code 29: Neutralizer water level abnormality

Noritz error code 29 indicates a problem with the neutralizer water level or, in other words, with the condensate drainage. The Noritz error code 29 is usually caused by a blockage in the drainpipe, incorrectly routed drain pipe, or using the wrong type of drain pipe.

Error Code 31: Inlet thermistor abnormality

Noritz error code 31 is an indication of a problem with the cold water inlet thermistor. If your Noritz tankless water heater displays an error code 31, you need to inspect the cold water inlet thermistor’s condition and replace it if needed.

While the error code 31 will appear on the remote control on some models, the unit’s display window will show an error code 311 or 312.

Error Code 32: Outlet thermistor abnormality

Noritz error code 32 means there is a problem with the hot water outlet thermistor. If your Noritz tankless water heater displays an error code 32, you need to inspect the hot water outlet thermistor’s condition and replace it if needed.

This error code may appear on the unit’s display window as error code 321, 322, or 323.

Error Code 33: Heat exchanger thermistor abnormality

Noritz error code 33 signifies a problem with the heat exchanger thermistor. If your Noritz tankless water heater displays an error code 33, you need to inspect the heat exchanger thermistor’s condition and replace it if needed.

This error code may appear on the unit’s display window as 331 or 332 while appearing as 33 on the remote controller.

Error Code 35: Exhaust thermistor abnormality

Noritz error code 35 (or 351, 352, 353, and 354 on the unit’s display window) is indicative of an exhaust thermistor problem. This error code is typically found on DV Noritz models. Check the exhaust wiring and ensure there are no shorts.

Error Code 45: Water leak

Noritz error code 45 means that water or excessive moisture has been detected in the unit. Stop the cold water valve and inspect for water or moisture. To fix error code 45, you may need to have a licensed contractor assess the condition of your Noritz tankless water heater.

If there are no visible signs of water or moisture, reset the unit by switching it off for at least 30 seconds. If the error code shows again after the reset, you will have to call for service.

Error Code 51: Gas Solenoid Valve Abnormality

Noritz error code 51 or 511 indicates a problem with the gas solenoid valve or its circuit. To fix this error code, ensure the valve’s connections are not damaged and set up correctly. Confirm the coil’s resistance is within spec. Replace the gas valve, the manifold plate, or the CB if necessary.

Error Code 59: Combustion abnormality

Noritz error code 59 means there is a combustion abnormality that is also associated with low input BTU. Inspect the gas pressure and check for any blockage or debris near or around the venting, fan motor, and burner chamber. If used at a high altitude, readjust the unit accordingly.

Error Code 61: Fan motor abnormality

Noritz error code 61 indicates an issue with the fan motor. To fix the Noritz error code 61, ensure the fan motor is working as intended. Measure the incoming voltage and check the operation of the CB. Replace the fan motor or the CB if necessary.

This error code can also be displayed as 611, 612, or 614.

Error Code 65: Main flow control valve abnormality

Noritz error code 65 points to a problem in the operation of the main flow control valve. To fix the Noritz error code 65, assess the main servo’s condition and function, and remove any debris and blockage from it. If the error doesn’t go away, replace the main servo.

Error Code 66: Bypass flow control valve abnormality

Noritz error code 66 means there is a problem with the bypass flow control valve. To fix the Noritz error code 66, assess the bypass servo’s condition and operation and remove any debris and blockage from it. If the error doesn’t go away, replace the bypass servo.

Error Code 67: AGM (Air Gas Mixer) abnormality.

Noritz error code 67 indicates a problem with the AGM (Air Gas Mixture) problem. Sometimes the AGM can get stuck, which results in an error code 67. To fix this error, turn off the unit for 20 seconds, power it back on. Check the AGM’s wiring condition if needed.

If the wiring is in good condition and the AGM remains not working even after resetting the unit’s power, it may need to be replaced.

Error Code 70: Circuit board abnormality

Noritz error code 70 (or 701 through 709) is a sign of a problem with the circuit board, which can often happen after reprogramming. In most cases, to fix the Noritz error code 70, you may need to replace the unit’s circuit board. This is not a DIY repair. You’ll need to contact a licensed plumber or contractor for correction.

Error Code 71: Gas valve drive circuit abnormality

Noritz error code 71 is an indication of a problem with the gas valve drive circuit. Error code 71 is often found in units powered with a modified sine-wave inverter instead of pure sine-wave. Check the voltage readings from the CB to the gas valve are within specifications.

This error code can also be displayed as 711 through 719 on some Noritz models.

A modified sine-wave inverter can, in some instances, even damage the unit’s electronics, so you may also do damage to the CB, in which case you should replace it.

Error Code 72: Flame rod detection circuit abnormality

Noritz error code 72 means that flame was detected without the unit firing up. Check your tankless water heater grounding and make sure there are no short circuits. To fix the error code 72, you may need to replace the flame detection circuit or the circuit board.

Error Code 73: Circuit board setting abnormality

Noritz error code 73 is an indication of a problem with the circuit board settings. Noritz error code 73 can be caused by connecting jumper clips or the dip switch while the unit is powered. To fix this error code, the unit needs to be powered off for at least 30 seconds.

If the error doesn’t go away after the restarting, you may need to have it inspected by a technician, as this error code can also be caused by a problem in the CB’s programming.

Noritz error code 73 can also show on the unit’s display as:

• Error code 731: Improper maintenance writer’s mode settings abnormality
• Error code 733 Dip switches setting abnormality
• Error code 734: CB abnormality

Error Code 76: Display Window transmission abnormality

Noritz error code 76 (or error code 768) indicates a problem with the display window transmission. Check the wiring condition between the main CB and the display’s CB. Replace the wiring or the main or display’s CB.

Error Code F76: Multi-system communication error

Noritz error code F76 means there is a problem in the communication system of multiple tankless water heaters. To fix a Noritz error code F76, you must restart the heaters, check the quick connect cord, and ensure that only one remote is connected to the two units.

If only one remote is hooked to the tankless water heaters and the quick-connect cables are in good working condition and not loose, and the error code persists even after the reset, get the units inspected by a licensed professional.

Error Code 90, 91, 99: Combustion abnormality

Noritz error codes 90, 91, 99 indicate a problem with the combustion. If your Noritz displays error codes 90, 91, 99, you should check the gas and gas pressure type. The flame color should be blue, not yellow, and you should remove any blockage near or around the air and exhaust vents and fan motor.

The unit should be switched off entirely for this error code to be reset. After powering the unit on, some models may require you to hold the Mode and Maximum Manifold Pressure Set buttons for about 5 seconds.

Error Code 92 or 93: Neutralizer life cycle warning

Noritz error codes 92 and 93 serve as a warning regarding the neutralizer’s life cycle. In the case of Noritz error codes 92 and 93, the neutralizer should be replaced as it is near the end of its life cycle. After the neutralizer has been replaced, you must reset the burner timer.

Error code 94, 941, 942: Exhaust temperature is too high

Noritz error code 94, 941, 942 means the exhaust temperature is too high. This error code is observed on DV models only. To fix it, you need to ensure nothing blocks the air inlet and the exhaust vent and that the heat exchanger is usually working and the cold water temperature is not too high.

Usually, you will find the error code 94 on the remote controller, while the 941 or 942 will appear on the unit’s display window.

Error Code 760: Remote controller transmission abnormality

Noritz error code 760 means there is an issue with the remote controller. To fix the Noritz error code 760, power off the unit for at least 30 seconds to reset it. Ensure that only one remote is connected to the tankless water heater system and check the remote controller wiring.

Keep in mind this error code may not show up on the display monitor of some units but only on the remote controller.

Error Code 901, 902, 903, 908: Air flow or combustion abnormality

Noritz error codes 901, 902, 903, 908 all relate to combustion or airflow abnormalities. Ensure that nothing blocks the air inlet, exhaust vent, fan motor and working as intended. Check the vent length adjustment and, if necessary, adjust for high elevation use. The CB or fan motor may need to be replaced.

These codes are related to the Noritz error code 90, which may be displayed on the remote controller, while these may appear on the unit’s display window.

Error Codes C, CF, H: Detect Scale Build-up in the Heat Exchanger

Noritz error codes C1 through C4 followed by a digit or a letter indicate a scale build-up in the heat exchanger. Error codes start with CF followed by a number or a letter indicating that the unit is locked. After reconnecting the electrical power, an error code H followed by two digits can also appear.

To fix these errors, replace any leaking parts if there are any. The heat exchanger may need to be flushed and cleaned, or even replaced.

A tankless water heater can last 15 to 20 years, and during that time, you’ll likely have at least one of these Noritz error codes. If you’ve recently brought a tankless water heater or looking to purchase a new tankless water heater, we invite you to bookmark this page.

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