Noritz Tankless Water Heater No Water Flow [Reasons + Fixes]

You often experience with your Noritz Tankless water heater no water flow which means water is not moving through the unit as it should be.

However, we have explored the following specific reasons behind the issue:

  • Closed water & gas supply valve 
  • A blocked water filter
  • Leakage problems
  • Clogged fixtures/ aerators
  • High demand of water
  • Crossed plumbing

Plus, the air in pipes and power issues are the villains that prevent your unit from getting sufficient water flow. 

noritz tankless water heater no water flow

Anyway, to troubleshoot those issues, go through our ultimate guide. You will definitely get your desired solution. Let’s go ahead…

Quick Solution For Noritz’s No Water Flow Issue

Before moving to any troubleshooting steps, we have sorted out an instant solution table based on our experience of the ‘No Water Flow’ issue with your tankless water heater. So, check out the table.

Names Of IssuesHow To Fix Instantly
Closed water supply valve> Check it out.
> Open it all the way.
> If needed, fix it by a certified plumber.
Blocked water supply/filter> Periodically clean the water supply line and clean the water filter with running water.
Gas valves are partially opened > Ensure the valves are opened fully.
Faulty flow sensor> Replace if the sensor is defective.
Crossed plumbing issue> If needed, reinstall the pipes correctly.
Power Supply Issue> Check out the power source.
> If the breaker has been tripped, just flip them up.
Sediment Build-up> Flush the accumulated sediment from your unit regularly.
Air in pipes line> To bleed air from pipes,  turn on the hot water faucet closest to the water heater until a steady stream of water comes out.
High demand for water > Consider installing more extra units with the existing ones.

Noritz Tankless Water Heater No Water Flow [Reasons + Fixes]

In this section, you will learn how to troubleshoot the leading factors that cause no water flow with your Noritz tankless water heater with effective fixes. So, start scrolling down…

1. Cut Off Main Water Supply To The Unit

If you aren’t getting enough water flow from your Noritz tankless water heater, higher chances are the water supply to the unit is cut off.  

Basically, when you turn on your unit, cold water passes through the supply lines. And then, the heating element heats up the water and fulfills your hot water demand.

But if the water supply is cut off, the cold water can’t reach the processing unit. And then, your unit won’t start due to the lack of proper water flow. 

Therefore, you can’t expect any water from your hot water fixtures. You might face this issue if:

  • The gas and water valve aren’t fully opened
  • Flow sensor can’t detect the water flow

The flow sensor is responsible for detecting the water flow rate and turning on the heating elements accordingly. If the flow sensor is faulty, it may not allow water to flow through the water heater. Anyway, you can simply fix this unwanted crisis.

How To Fix:

To get sufficient water flow, first, we highly recommend you check the main water supply valve. Turn ON the water supply valve fully to let the water supply flow to the unit. 

It would look like the below picture:

inlet water supply valve

If the water supply line can’t bring any luck, a partially closed gas supply valve may be a cause behind the issue. In fact, the gas valve should be opened fully like.

Noritz tankless water heater gas valve

When there is no problem with the water supply and gas valve, we suspect the flow sensor is the next culprit. 

In this case, carefully remove the front access panel and inspect the flow sensor from the inside. You will find it clogged with carbon deposits or debris. Clean the deposits with sandpaper or remove the debris under running water. But for a damaged flow sensor, replace it with a new one.

If you can’t fix the issue yet, call a professional plumber to resolve the problem.

2. Clogged Water Inlet Filter

The water inlet filter is an essential element in the Noritz tankless water heater that prevents sediments to enter the heater inside through filtering. By doing so, this element helps to maintain a steady water flow to the unit. 

clogged water inlet filter

But as it is always in contact with hard water minerals, clogging with sediment deposits is quite obvious. If this happens, you will never expect to have fluent water flow through the unit which causes a reduction or complete stoppage in water flow. 

How To Fix:

To ensure restriction-free water flow throughout the unit, clean the water filter screen following the below procedures:

  • Close the water supply valve in a horizontal way.
  • Open the hot water faucets fully.
  • Remove the inlet, outlet caps, and both drain plug caps
  • Place a basket underdrain plugs to collect residual water
  • Detach the water filter screen out of the inlet.

Now, clean the water drain valve with a brush and wash it under running water. Through this process, you can remove any accumulated debris and sediment from your filter. Next, let the filter dry well. You can use a towel to dry it.

clean the water drain valve

Finally, reinsert the filter back into its position. Hope you won’t face any more water supply crisis.

3. Faulty Flow Sensor

A faulty flow sensor is another villain in preventing the water flow rate. 

Typically, the flow sensor detects the water flow rate and turns on the heating elements accordingly. But if the flow sensor is defective, it won’t permit water to flow through the unit. 

How To Fix:

To fix the flow sensor issue on the Noritz water heater, follow the below steps:

  • Turn off the power of the unit.
  • Locate the flow sensor near the cold water inlet. (Location may vary on model)
  • Once you’ve located the sensor, disassemble it from the connection.
  • Now, carefully clean the sensor with a soft brush or cloth to remove any debris. Don’t apply any harsh chemicals or abrasive materials so that it mayn’t damage.

If the cleaning effort doesn’t bring any luck, test the flow sensor for continuity with a multimeter. If there is no continuity, the sensor is faulty itself and needs to be replaced with a new one. 

And ensure the new sensor is compatible with your Noritz model. After replacing one, connect the wires tight.

Next, turn on your unit and check the sensor working properly.

Note: If you aren’t good at replacing the sensor, contact a licensed plumber or HVAC technician to replace the flow sensor.

4. Leakage Issues

When the water supply is fine but there is no water flow, we confirm water leakage is the next cause that restricts the proper water flow of your unit. 

noritz tankless water heater water leakage

How will you know your unit gets leaked? Sometimes, the unit can get leaked in its bottom part or connected pipes. If the bottom part leaks, you will see liquids near the lower part of the unit, and for pipe leaks, you will notice the adjacent walls are wet.

How To Fix:

A troubleshooting step on leakage issues mainly depends on which equipment is leaking and why.

So, check out and verify any leakage around the water supply lines. If you can detect the external leakage or the valve is leaking water, shut off all sources of water which are connected to it and try to repair it by re-tightening or replacing the leaked parts.

But for internal leakage, call a certified plumber to handle the case.

If you face the same issue after repairing the leaks, check whether your water heater fixtures become clogged or rusty due to hard water.

5. Sediment Build Up

Sediment buildup in a Noritz water heater is a potential cause that has a significant impact on the flow rate of water through the unit. Sediment is a common scene in hard water areas, as it contains high levels of minerals like calcium and magnesium. 

Over time, the accumulated sediment causes blockages or clogs inside the heater. As a result, this issue reduces the optimal water flow rate and can even shut off your unit completely. So, take a protective measure against it.

How To Fix:

To protect the heater against sediment accumulation and to maintain the water flow rate, flush your Noritz heater periodically.

In fact, flushing involves draining all the water. It will help to dislodge any sediment that has built up inside.

In addition, install a sediment filter on the incoming water line. It will protect the sediment from entering the water heater. Read this article on how to flush your Noritz water heater

6. Clogged Fixtures/Aerators

A clogged water fixture/ aerator may cause low water flow. Typically, your Noritz tankless water heater has an inlet screen filter to catch debris that prevents your fixtures from getting blocked or clogged. 

But over time, if the debris accumulates in the filter, it can’t protect the fixture from getting clogged or blocked. This may happen especially if you live in a hard water area and open the fixtures partially. 

fixture from getting clogged or blocked

As a result, an excessively scaled build-up with a water faucet/tap prevents smooth water flow. Even with restricting water flow, this issue reduces hot water pressure simultaneously. The scaled faucet looks like this:

scaled build-up with a water faucet

And then, you won’t expect a full flow of water when there is a scaled deposit in the aerator or the shower head. 

How To Fix:

To fix the case, first head shower faucets of your water heater.

Then, disassemble the aerators from the faucets and clear out the scaled deposits to restore water flow. Use a toothpick or paperclip to remove the deposits or you may soak it in vinegar as well.

After completing the cleaning, replace the aerators with the correct position. Finally, make sure you have opened the fixtures fully.

Also, it is recommended to clean the aerator and the shower head regularly to avoid such low water flow crises.   

7. High Demand For Water

A tankless water heater supplies on-demand hot water as per its GMP or gallons per minute. But when your unit crosses its limit level due to overload, you will face insufficient water flow.

Plus, if the water demand is more than the heater can comfortably heat up, the heater will affect the water flow rate. The system will also result in no water pressure.

Suppose you are in the shower, cleaning dishes, or doing other domestic chores at the same time. Chances are that you will face a No Water Flow issue randomly.

How To Fix:

To avoid overloaded issues, just make sure how many people are using water fixtures at a time. So, ensure you’re opening the supposed water fixture simultaneously.

If you have a high demand for water, you can upgrade your water heater by adding more tankless units to the existing unit. Hope you won’t face water flow issues with your water heater.

8. Crossed Plumbing

Last but not least, reversed/crossed plumbing is regarded as an issue for insufficient water flow for Noritz tankless water heater. There may be a problem with leakage and blockage in the pipes, which is preventing water from flowing through the water heater.

To resolve crossed plumbing, simply investigate if the plumbing system is fine for running water properly. And check whether the hot and cold pipes have been installed correctly. 

In case of reversed plumbing, you will need to reinstall the lines – the hot water pipe should be set to the hot and the cold line should be installed to the cold water supply line.

How Does Noritz Tankless Unit Recirculate Water

Typically, a tankless unit directly heats water without using a storage tank and instantly provides hot water to use. Let’s know the water recirculation process step by step.

  • The power supply is turned ON
  • The hot water fixture is opened
  • Cold water flows through the heater
  • The Flow sensor detects the water flow
  • The burner ignites automatically
  • Water circulates through the heat exchanger (Either the gas burner or electric elements heat the water).

And, finally, you open the hot water taps and use hot water as per your demand. 

How To Measure Noritz Water Flow Rate

You can simply test the water flow rate by yourself. Just open multiple hot water fixtures for passing through the required water flow of the unit. Whatever, follow and complete the below tips to do the test effectively.

  • Take a 1-gallon water tank or basket and a timer device like a stopwatch or smartphone.
  • Turn your water tap
  • Calculate the time until water fills the container using a timer device.
  • Divide the number of minutes it took to fill up the bucket.

For example, it required 20 minutes to fill up a one (1) gallon bucket. Now, divide the amount by the taken minutes. You will get the calculation as per minutes. So, your per-minute gallon is the water flow measurement of the water heater. 

Here, you can know the water flow rate with your Noritz water heater.

Name Of Noritz ModelWater Flow Rate Per Minute (GPM)
Noritz NRC1111-DV> Maximum flow rate of 11.1 gallons per minute (GPM)
Noritz NRC661-DV> Maximum flow rate of 6.6 gallons per minute (GPM).
Noritz NRC98-DV> Maximum flow rate of 9.8 gallons per minute (GPM)
Noritz EZ Series> These tankless gas water heaters include models with flow rates ranging from 5.9 to 11.1 gallons per minute (GPM).

Whatever, we strongly suggest you operate your water heater within the recommended water flow range between 0.5 GPM to 7.5 GMP.  


As per the manufacturer’s guide, most models operate with a minimum flow rate of 0.5 GPM. Anyway, a tankless unit should have the minimum water flow rate for initial operation.

What may occur if I operate my Noritz with a low flow rate?

Your Noritz tankless water heater operating with a low flow rate can cause several problems. Such as you won’t get hot water. Plus, your unit will face overheating issues, reduce efficiency and bring damage to your unit.

How to increase the water flow rate with a tankless unit?

To increase the water flow rate with your Noritz heater, check the water pressure at the main water supply valve and adjust as needed. Plus, ensure your heater is running through a minimum flow rate.

Final Thought

While using your Noritz tankless water heater, you face a problem with a sudden fall in water flow.

To troubleshoot it, cleaning the essential parts like the inlet water filter, and flow sensor should be your first prioritized steps.

Plus, make sure you’ve opened the gas and water valves fully and your unit is operating through the recommended water flow rate.

Fortunately, we have guided you on how to fix your Noritz tankless water heater no water flow-related issues. Yet, if you have any queries about our troubleshooting guide, feel free to know us through the below comment section.

Note: Read our guide on why Noritz tankless water heater leaking and how to fix it.

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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