How to Fix Noritz Water Heater Error Code 90?

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Noritz Water Heater Error Code 90

If you are out here reading the following article on, “How to fix Noritz Error Code 90?”. It is pretty obvious that you must be using a Noritz Tankless Water Heater at your place and have recently come across the Error Code 90, for which you need a solution ASAP!

Now, for some reason if your Noritz Water Heater is showing the Error Code 30. It might very well be due to “Bad Combustion”, as mentioned on Notriz’s very own official website. 

This error, one could say, is fairly a very common error code out there, experienced by most Noritz heater users out there. Hence, once you know how to solve the issue, life should become much easier for you.

Why is my Noritz Water Heater showing Error Code 90?

As have been already mentioned once above, when we see the Error Code 90 flashing on your Noritz Water Heater device. It basically means that there is an issue with the Combustion or Combustion unit of the device.

Now, it is very important that we first look at the main reasons behind such an error to occur in the first place, before having a look at the solutions.

This way while troubleshooting the Error Code 90 for Noritz heater, not only will we get a better understanding of the problem but can also deal with it much more efficiently and effectively. 

Having said that, when talking about the Combustion problem with the Water Heater unit. There can actually be quite a number of reasons responsible for such an issue to occur. 

It may be due to an insufficient amount of gas pressure being generated and supplied to the unit, or venting issues caused by faulty installation of pipes inside the heater.

All of the reasons which in one way or the other deal with the air, gas or venting problems inside the machine can be considered potential causes for the Error Code 90 to show up on your respective Noritz Water Heater devices.   

So, now that you have a somewhat general idea of what potential causes there might be for your Noritz Heater to show the following Error Code. I believe it is time to next look at the Ways or Steps to solve the Error Code 90 in your Noritz Water Heaters.

How To fix to solve Noritz Error Code 90?

The following section may be considered a guide to help you figure and narrow down the main reasons behind the error.

After which you can go on following the required solutions and steps needed to solve the particular issue to help fix the error code and prevent it from returning in the future again. 

Now, when troubleshooting and narrowing down the issues causing the particular error. It is very crucial and important that you consider and keep an eye on the Maintenance Monitor at all times. 

It is only with the help of the Maintenance Monitor, that you will be able to accurately point out the actual problem or issues causing the problem and take necessary steps to solve it thereafter.

So, the way you would be accessing MM (Maintenance Monitor) now, would most probably with the help of your device’s remote control.

Fix 1: get into Maintenance Monitor Mode in Noritz

Below, let us have a look at how to open up Maintenance Monitor Mode on your Noritz remote unit and view it to decide what issue is causing the problem. 

  • For the very first step, before entering MM mode, you will need to first keep a note on the set temperature.
  • Then, turn off the remote and next, press and hold the UP and DOWN button until ‘03’ comes up on the display screen.
  • Next, turn on the unit by pressing on the power button, so that the Priority led light and the Power led light are illuminated.
  • Then, go on pressing the UP button, until the value in the MM screen reaches to 31
  • Once you reach the value 31, leave the UP button and you should be able to see the temperature of the water leaving the water outlet.

Hence, in this way you should be able to determine the outlet temperature as well as the fan speed by logging to MM31 and MM49 respectively. 

You will get a better understanding of this as you go on reading the section and steps as described further below.

Fix 2: Check water temperature on Noritz with MM31

  • Now, once you reach the value 31 as mentioned in the last step above, next you will be able to see the outlet water temperature coming out of the facet. 
  • Here, as the water keeps coming out of the facet, the temperature should keep on increasing further till it reaches the temperature you had initially set in the device.
  • It is important to note here, that if everything is fine with your heater. The value of the displayed temperature on your screen should be in between +2 or -2 degrees of the initially set temperature value.
  • Hence, if the value is anywhere in between 2 degrees on the upper scale or lower scale. It means that the burner unit inside the unit as well as the facet is working fine.
  • However, if the value being displayed is further less than the (set up value – 2 degrees). Then, there might be a possibility that the unit is not getting enough gas being sent to the burner. Hence, water inside the unit is not getting heated up to the desired amount. 

Usually, gas related issues are mainly caused by plumbing issues. Thus, should be taken care of by a professional at this part, if any kind of maintenance with the pipes are required. 

Otherwise, a couple of steps for Regular and Periodic Maintenance as shown below should do the trick.

Fix 3: Check the fan speed and airflow on Noritz with MM49

To check whether the fan speed is working normally and airflow is adequate, you will need to follow the steps as shown below:

  • For the initial steps to open up the MM mode, you will need to follow the same steps as shown earlier for logging into the Maintenance Monitor mode up until you reach the second last step.
  • Then, instead of just going upto 31, keep on pressing the UP button till you reach the value 49 and then leave the button.
  • After this, if your fan is running normally, then it should display the value 100
  • However, if the value is anything more than 100. Then, that would mean that there is a problem with combustion where the amount of fresh air being displayed may be less than that is required. Due to which the fan is trying to compensate for the influx of air by increasing the fan speed.  
  • Similarly, if the value is lower than 100. Then, that would mean that there is a problem with the fan itself and it needs to be repaired.

Fix 4: Steps to perform periodic maintenance on Noritz

Once, you have determined what might be causing the Error Code 90 to show up on your Noritz heater device. It should become fairly easy to deal with the issue by making the required changes or maintenance as shown in the steps described in the video below.


Hence, in this way if the problem with the device is not a critical one and does not involve any kind of serious physical or hardware damage. Then, you should be able to resolve it by going through usual periodic maintenance of the unit from time to time. 

However, if the problem is caused due to a serious issue with the unit or piping. Then, having a professional look into it would be more convenient for you to solve the issue more efficiently and effectively.

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A tech enthusiast who is always curious to learn and absorb facts and data in the world of science and technology as well as tries to share his opinion on what he thinks might be fun to know for others. Loves to dive deep into nature when not busy exploring the world of tech.