Noritz Code 90

How To Fix Noritz Code 90?

Noritz Code 90 indicates there is a problem with combustion. Issues with the gas, air, and venting cause the water heater to throw the error code 90. 

And this guide will help you determine if the issue is one of the problems I mentioned. Plus, I will walk you through the steps to erase the diagnostic code 90. 

So, let’s get started. 

Table of Contents

What Is Code 90 On Noritz Water Heater?

Code 90 on the Noritz Water Heater stands for combustion abnormality. In simple words, the water heater is not burning properly because of the problem with the gas, air, and venting.  

Fortunately, you can easily determine whether those are the issues I mentioned responsible for poor combustion or not. And the test that will help you discover the reasons behind error code 90 is maintenance monitor mode. 

To go into the maintenance monitor mode, follow the steps I described below: 

  • Note the set temperature of your unit before entering maintenance monitor mode.
  • Turn off the remote controller by pressing the Power (on/off) button. 
  • Press and hold both the up and down buttons together until the 03 code appears. 
  • Turn the water heater back on so the power light and the priority light comes on. 
  • Keep pressing the up button until you get to maintenance monitor 31 and you can see the water temperature setting at the outlet. 

And now, you are in the maintenance monitor mode. 

Noritz Code 90: The Reasons & Solutions

Below, I will walk you through the steps to determine whether there is an issue with gas, air, or venting behind the code 90. 

Gas Supply Issue

Get access into maintenance monitor mode by following the steps I mentioned. Once you get this mode, turn on the faucet you want to test. 

The burner light will turn on once the unit has fired up and you will see the water temperature start increasing. Once the water heater hits the set temperature, it will maintain the temperature within two degrees. 

For example, if you set the temperature to 120, the MM31 should be limited between 118 to 122. And it’s normal. 

But if the MM31 reading is lower than the set temperature, I bet there is an issue with the gas supply that causes the unit to not heat the water properly. 

Here gas supply issue means: 

  • Getting insufficient gas into the burner
  • Obstructions in the manifold
  • The burner gets clogged by dirt or fuel residue
  • Improper inlet gas pressure

How To Fix Gas Supply Issues:

To begin with, ensure you fully turn on the gas valve. If you don’t fully open the gas valve, sufficient gas will not flow into the burner.  To turn on the gas valve, turn it counterclockwise. 

Turns out, if the burner gets clogged, you will not receive enough gas in the burner for proper combustion. To clean the burner, complete the following steps: 

1. Ensure you turn off both the electric supply and the gas supply to the unit. Then, use a Phillips head screwdriver to remove the screws that hold the front cover in place and set it aside. 

2. Disconnect the manifold connection from the wiring harness by pressing the top connector. 

Detach the gas manifold connection
*Detach the gas manifold connection*

3 Now, it’s time to remove the seat clamp. In this case, hold the gas manifold pipe in place and pull out the clamp. 

Pull out the seat clamp
*Pull out the seat clamp*

4. Remove the gas manifold by unscrewing the four large screws. Once you remove those screws, you will see the manifold comes loose but it will not fully release. So, push up on the gas manifold pipe and remove the gas manifold to expose the burner. 

Unscrewing the manifold screws
*Unscrewing the manifold screws*

5. Use an air compressor to blow away dirt and debris from the burner chamber and clean it evenly. 

Cleaning the burner using an air compressor
*Cleaning the burner using an air compressor*

6. Also, don’t forget to inspect the gas manifold. If needed, clean the manifold orifices with a paperclip.  

7. Once you clean both the burner and gas manifold, reassemble the unit following the steps in reverse. 

And last not the least, check the gas inlet pressure and adjust the pressure if needed. The following tutorial will help you in this case: 

Air or Venting Issues

If your water heater is hitting the set temperature on MM#31, you should go to MM#49 as there is no issue with the gas supply. 

Note: Ensure you are in maintenance monitor mode by following the instructions I mentioned earlier. 

Keep pressing the up button until you get the maintenance monitor 49. This stands for fan speed correction. 

If the front cover is on and the unit is under normal operating condition, the MM#49 should always read 100. Anything higher than this value like 105, 106, or 107, understand there is an issue with air or venting. 

In other words, your fan is overworking and it fails to pull in fresh air for proper combustion or expelling the exhaust from the water heater. 

Several reasons are to blame if there is a problem with the air or venting, including: 

  • Venting length is too long with many elbows
  • Set up the DIP switches for venting or high-elevation improperly
  • Venting gets clogged by dirt, debris, snow, or dead birds
  • Air screen filter gets clogged by lint
  • Fan is dirty 

How To Fix Air or Venting Issues: 

Start with checking venting length. If it’s too long, I recommend you check the installation manual for maximum venting runs. It will be better to call a certified plumber to re-install the venting according to the manufacturer guideline. 

Secondly, ensure you set up the DIP switches for venting or high elevations properly. If not, check the manual and adjust the DIP switches accordingly.  

Thirdly, inspect the venting for blockage and release the restrictions from it if needed. 

Finally, I recommend you read this guide on Noritz Tankless Water Heater Maintenance to learn how to clean the air screen filter and the fan. 

How Do I Fix Noritz Error Code 90?

Go along with these steps to erase the Noritz Code 90:

  • Determine what causes the unit to throw the error code 90 by following the instructions I mentioned above.
  • Resolve the issues responsible for the error code 90. 
  • Reset the unit. In this case, unplug the unit from the electric connection, wait 30 seconds, and plug the unit into the electric outlet. It will reset the Noritz error code 90. 


How do I clear Noritz error codes?

To clean Noritz error codes, follow the below steps: 

  • First determine the reasons that cause the unit to pop up a specific error code.
  • Once you figure out the root cause of an error code, resolve that issue. 
  • Reset the unit. 

If you don’t know how to reset the Noritz Water Heater, check this article on Noritz Tankless Water Heater Reset Button

Why does my Noritz water heater keep shutting off?

Noritz Water Heater keeps shutting off due to the following reasons: 

  • Electric problems
  • Issue with gas supply 
  • Flame sensing rod gets dirty 
  • The heat exchanger gets damaged
  • The flow rate is too low

To resolve those issue, read this article and get your water heater ready to heat the water. 

Is there a reset button on my tankless water heater?

No, there is no reset button on the Noritz tankless water heater.


I hope this guide will help you solve the error code 90 on Noritz Tankless Water Heater. What you need to do is- just follow the instructions I mentioned. 

If you need further assistance, don’t hesitate to contact the Noritz Technical Support Team at 866-766-7489. Good Luck!

Read Also:

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *