Noritz Tankless Water Heater Won’t Turn On [Why+ How To Fix]

Your Noritz tankless water Heater won’t turn on or keeps shutting off due to the following major culprits:

  • Tripped circuit breaker
  • Insufficient gas supply
  • Power supply Issue
  • Too low water flow rate
  • Poor airflow to the unit

Whenever you’ll encounter such an issue, make sure you’ve plugged your water heater into a well-operational power outlet.  Check for tripped circuit breaker and reset it. Above all, open the water supply valve and hot fixtures all the way to turn on your unit. 

noritz tankless water heater won't turn on

But if still the problem isn’t resolved yet, we suspect other villains like, a clogged air filter screen and plugged-up heat exchanger are behind this malfunction.

Therefore, keep on reading our troubleshooting guide to find out the root reason why your unit isn’t turning on and fix them by yourself.

Table of Contents

Noritz Tankless Water Heater Won’t Turn On/Keeps Shutting Off [Reasons + Solutions]

In this guide, we’ll walk you through every step so you can solve your Noritz tankless water heater shutting off or not turning on issues. Let’s get started here!

Note: Read our guide on why Noritz tankless water heater problems & error codes and how to fix it.

1. Tripped Circuit Breaker

A tripped circuit breaker is the leading factor for why your tankless water heater won’t turn on or fails to stay on. There are several factors that would trip the circuit breaker constantly. For instance:

tripped circuit breaker
  • The heater produces excessive temperature
  • Short circuits in the electric lines
  • Or even malfunctioned circuit breaker is the culprit itself. 

When the circuit will trip, you will never expect to turn on your  Noritz water heater. 


Firstly, for a tripped circuit you will have to reset the breaker. To do so, simply flip up the tripped switches to the ON position. By doing so, your heater should turn on. 

If not, check out all the wiring connections around the electric lines to verify they are in good condition.

Secondly, to prevent a circuit breaker that constantly trips, you need to troubleshoot the overheating issue. Here are simple procedures you need to apply:

  • First off, ensure you have set the temperature of your water at the recommended level. You can go through the manual for your Noritz model. 
  • Secondly, inspect your circuit breaker whether it is out of order or broken. If so, replace it ASAP to run your heater properly. We highly recommend you call a certified electrician to deal with the issue. 
  • Apart from all the above, a clogged heat exchanger is another major villain behind the overheating problem that causes the breaker to trip. You can simply solve this issue by descaling the heat exchanger.

Go through the below cleaning procedures to know how to flush a Noritz’s heat exchanger.

How To Flush Noritz Tankless Water Heater

Flushing is a regular part of Noritz maintenance. Start your descaling session by turning off the gas valve. Take your cleaning accessories and complete the following steps to descale your heat exchanger. You will need:

  • Food-grade white vinegar (1-2) Gallons
  • 5- Gallon size bucket
  • 6HP submersible utility pump
  • Two connection drain hoses (¾ inch) 

After managing the above element, flush your tankless unit by following the below simple processes:

Step #1: Turn off both the inlet and outlet valves. Take out the drain cap from both pipes. 

Step #2: Attach one drain hose (H1) to the cold water drain valve and one hose (H2) to the circulation pump. When done, place the pump with the connected hose into the five-gallon bucket. 

Step #3: Now take another drain hose and connect one end to the hot water drain valve and place the other end into the bucket.

Step #4: Pour the white vinegar into a bucket in a way so that the pump is completely submerged.

Step #5: When done, open both drain valves (V3 and V4) and turn on the pump for at least an hour. 

Step #6: After that time, turn off the pump. close the cold water drain valve and remove the hose from it. Replace the cap. 

Step #7: Now,  place the hot water drain hose into another bucket. Open the cold water main valve. Let your water heater flush out with fresh and cold water for 5 minutes. 

When done, turn on the drain valve and remove the drain hose. Now turn on the water and gas supply to the unit.

2. Insufficient Gas Supply

Your Noritz tankless water heater (gas-operated unit) won’t power on if the unit doesn’t get a continuous flow of sufficient gas supply.

Basically, the gas supply will be interrupted during operation unless you turn on the gas valve fully.

noritz tankless water heater insufficient gas supply

On the other hand, improper-sized gas meters prevent your heater from supplying enough gas to the unit. However, this problem isn’t too tough to fix.


To solve the gas supply issue, ensure first, you have paid up your gas bill. And if you have an LP gas-operated water heater. Confirm that there is sufficient gas in the tank for proper combustion. 

Then, check the gas supply valve position and make sure it is fully opened to the “ON” position. For instance, the valve lever should be parallel to the piping position to supply trouble-free fuel during operation.

Above all, confirm that you have fed the right type of gas. For this, you can check it on the rating plate of the unit to ensure either your water heater demands natural gas or propane for ignition.

Next, don’t forget to measure the gas pressure for your water heater using a gas monometer. Let’s have a look proper gas pressure required for a functional water heater.

Noritz Tankless Water Heater Gas Pressure

Type Of Water HeaterRecommended Gas Pressure
Natural Gas Operated UnitBetween 5” W.C. to 10.5” WC
Propane Operated UnitBetween 8” WC to 13.5” WC

In case the gas pressure of your heater is not in this range, you need to size up the gas meter accurately to have a proper gas pressure. 

If needed, seek help from an expert plumber to adjust gas pressure. Watch the below video will be helpful to check & adjust the gas pressure.

3. Electric Supply Issues

An interrupted electric supply is the next major reason that prevents your Noritz water heater from coming on. A functional electric power panel is a must to run your water heater smoothly.

electric supply issues

You may experience this unwanted situation due to any of the following reasons:

  • The power button is turned off
  • Grounded improperly or loose wiring connection
  • Improper circuit panel
  • Non-functional electric outlet

Typically, the Noritz water heater requires 120 volts at 60 Hz of electric supply for actual operation. Hence, the unit won’t turn on unless it gets the required power supply. 


First, ensure you have plugged your water heater into a functional wall outlet. If needed, test the voltage of the unit by plugging your phone charger and verify whether the outlet is going on fine. Then check whether the power switch is in the ON position. 

Check out the fuses as well. If they get damaged, you should replace the blown fuses immediately. 

If still your water heater doesn’t turn on, verify the wiring connections of your water heater are in perfect working order. 

Finally, confirm that you use an appropriate circuit so that it can consume power up to 360 Hz. Hope the power supply issue will be solved.

If you don’t have enough electricity supply to your water heater yet, we will highly recommend you hire a certified electrician to resolve your troubles.

4. Low Water Flow Rate

A considerable water flow rate is required to activate a tankless water heater. Like every tankless water heater, Noritz has a minimum water flow rate. In this regard, your water heater isn’t an exception to that.

low water flow

Typically, a Noritz tankless water heater required a minimum water flow rate of 0.05 GPM to ensure optimal operation. 

But, when the flow rate is less than the demand, the unit won’t turn on. Whatever, we have identified several below culprits for the issue. They are:

  • Clogged water drain valves
  • Reverse/cross plumbing
  • The flow sensor gets damaged
  • Low water pressure 


You can simply fix the issue by increasing the water flow rate to your water heater. For instance, make sure you have gone through the followings:

First up, open the water shut-off valve fully in order to allow trouble-free water flow to your water heater. Also, open multiple hot water fixtures for passing through the required water flow of the unit.

Next, investigate the water drain valve for blockage. The valve tends to be blocked by sediment and debris over time. So, inspect the valve and clean it properly. 

.Plus, take an overview of the flow sensor. If you find it damaged or cracked, replace it.

Nonetheless, reverse plumbing can reduce the water flow. For this cross plumbing, verify the hot water and cold water lines are to the point.

Finally, measure the water flow range of your water heater whether it is between 0.5 GPM to 7.5 GMP. It should neither be so high nor too low as per the demand of your heater. 

Above all, avoid using too many hot water fixtures at a time that goes beyond your water heater’s minimum hot water demands. 

5. A Blocked Exhaust

Last but not least, a blocked venting system also affects your water heater’s normal operation. Especially when your water heater isn’t responding well as it should, a blocked vent may be a major sign behind the issue. 

noritz tankless water heater blocked exhaust

Due to air blockages, there won’t be sufficient airflow through the init. This term overheats the unit which causes the circuit breaker to trip. And ultimately you can’t turn on your water or experience keeps turning off the unit rapidly. 

Despite the venting, the clogged air filter screen is another major culprit for poor airflow to the unit.


Start with investigating the exhaust venting pipes of your water heater. You will find stuck dirt and debris there. Take a vacuum cleaner and suck the debris from the vents.  

If you find it difficult to reach any part of the vent, you can use a duct cleaner either. After cleaning, ensure a proper installation of the venting.

When done, remove the front access panel of your water heater and locate the air filter screen. Unscrew it from the connection and take it out.

Remove the hard particles stuck in the filter screen with a wire brush. Then wash it under running water. Let it dry and reassemble the filter back in place. Make sure it is secure and tightened enough to its place. 

How To Reset Noritz Tankless Water Heater

When your Noritz water heater goes into trouble with starting on, you can reset your Noritz tankless water heater to resolve the issue. It may save you a huge maintenance cost and time. Follow the effective steps to reset the unit.

Step #1: Disconnect the power connection from your water heater.

Step #2: Wait 30 seconds to reset the unit.

Step #3: After that time, plug the unit back into the power connection. Then, turn on the water and gas supply and your water heater should work smoothly.

How To Properly Turn On Noritz Tankless Water Heater

You can simply turn on your Noritz water heater by following the steps.

  • Keep the water supply valve to the piping in a parallel sequence.
  • Turn On hot water fixtures to ensure the water is available and then, close it.
  • Open the gas supply valve right to the supply lines.
  • Switch On the power of your heater.
  • Push on the on button and set the temperature to 125 F. would be the best setting. Now, open the hot water faucets.

Hopefully, your water heater will turn on for super operation.


Why does my Noritz tankless water heater shut off during the shower?

Your Noritz water heater shuts off during the shower due to low gas pressure or low flow rate. Plus, a defective thermocouple, clogged water line, or faulty heating element may be causes for the issue.

Why does my tankless water heater attempt to ignite but fails?

You turn your Noritz heater and it tries to ignite but fails. This may occur if there is air in the gas lines or other valves. Try to reset the unit to fire up your water heater.

What is the normal lifespan of a Noritz tankless water heater?

A normal life span of a Noritz water heater is 12–15 years under warranty. However, with regular maintenance, you can keep your heater in place for another 20 years.


Already, we have discovered that tripped breaker, insufficient gas supply, and low flow rate are mainly responsible for your Noritz tankless water heater not turning on or keep shutting off. 

However, fortunately, we disclosed each of the culprits that will help you to resolve the shutting-off issue.

Now, what you will need, just follow our ultimate troubleshooting steps as mentioned throughout the guide.

And yet, if you encounter any issues turning on your tankless water heater, let us know by throwing your comments. Our experts will reach out to you ASAP with a simple solution.

About Phillip

Phillip is an HVAC guy & has convenient skills in the fireplace, heater, stove & other heating systems. He has been working and writing in this field for the last 5 years. He is really passionate about writing & share his expertise through his writing to help others. More about us.

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