Noritz Tankless Water Heater No Hot Water

Noritz Tankless Water Heater No Hot Water

Your Noritz Tankless Water Heater will produce no hot water due to the following reasons: 

  • Partially open the gas and water supply valves.
  • Water supply at the unit is cut off.
  • Gas supply is cut off
  • Not enough gas in the tank
  • Water drain valve filter gets clogged

Throughout this article, I will walk you through each of those culprits and let you know how to fix them. So, stay in tune with me till the end. 

Table of Contents

Noritz Tankless Water Heater No Hot Water [5 Easy Solutions]

From this chapter, you can discover the solutions that will help you fix the ‘no hot water’ problem. 

1. Partially Opened Gas And Water Supply Valves

Sustained or continuous flow of water and gas to the unit is a must. If your Noritz water heater doesn’t receive uninterrupted gas and water supply, it will never heat the water. And the culprit behind getting interrupted gas & water supply is to not fully open the gas valve and the water supply valve. 

How To Fix: 

Open both the gas valve and the water supply valve fully and it will solve the issue. Just take your eyes on the inlet water supply valve and ensure you fully open it; not partially. The water supply valve will be inline just like the following picture if when you fully turn it on: 

position of a fully opened water supply valve on Noritz

Next, inspect the position of the main gas supply valve. Then, turn it to the open position fully if needed. This is how the position of a fully opened gas valve looks like: 

position of a fully opened gas supply valve on Nortiz

2. Water Supply At The Unit Is Cut Off

Tankless water heaters, whether it’s from Noritz or Rinnai, won’t start if there is not enough water flow or the water supply at the unit is cut off. In Noritz, the minimum water flow rate is 0.5 GPM. And this is an intrinsic characteristic of tankless water. 

If you don’t fully open the water supply valve. Sufficient water will not flow to the unit. Consequently, you can’t turn the unit on. Guess what, not turning on the water heater means no hot water. 

Turns out, every tankless water heater comes with a flow sensor. It senses the flow of the water and lets the unit fire when it detects the minimum flow of the water is flowing to the unit. 

If this sensor gets damaged, it will signal the unit that there is insufficient water flow. As a result, you will get no hot water out of the unit. 

How To Fix: 

First, ensure you fully open the inlet water supply valve. If not, turn on the water supply valve to let the water flow through the water heater. 

If turning on the water supply valve brings no luck, you should inspect the flow sensor. I highly recommend you call a certified plumber to check the flow sensor. If it gets damaged, replace it with a new one. 

Forget to mention that you should also check the main water supply line of your house. If there is any issue, it will affect the water supply at the water heater as well. 

3. Gas Supply Is Cut Off

The Noritz Tankless Unit requires a sufficient amount of gas supply for proper operation. If no gas is flowing at the unit or gas meter, it’s impossible to light the unit. In short, no gas means no hot water.

Typically, the gas supply at the unit is cut off because either the gas valve is in the off position or the gas meter shut-off valve is off. 

How To Fix: 

Start with checking the gas supply valve on the unit. If it’s in off position, turn it counter-clockwise to let the gas flow to the unit. The gas supply valve will be inline on the pipe when you fully open this valve. 

Next, locate the gas meter shut-off valve on the gas meter. Ensure you fully turn it on. If not, set it to the On position. 

4. Not Enough Gas In The Tank

If you have a propane-powered Noritz water heater, it will be a common issue to not have sufficient gas in the propane tank. Without enough gas in the tank, you will never power the tankless unit. 

Similarly, if you feed multiple appliances like the gas stove from the same tank, the gas in the tank will end quickly. 

How To Fix:

First off, make sure there is enough gas in the tank. You can easily check it by lifting up the tank. If it seems light, you should refill the tank with propane gas. 

Second, ensure you run only the water heater from a specific propane tank. Use another gas tank to operate other appliances like the gas stove. 

5. Water Drain Valve Filter Gets Clogged

A clogged water drain valve filter is another culprit that can also throw a wrench into work. If the drain valve filter gets restricted by dirt or mineral deposits, water will not flow through the unit trouble-freely.

And without a proper water supply, the Noritz Water Heater can’t be operated. In other words, you will get no hot water out of the unit if the drain valve filter gets blocked. 

How To Fix: 

Cleaning the water drain valve filter will be a simple fix to this issue. Follow the below procedure to remove deposits from the filter:

First off, close the water supply valve. To close the water supply valve, you should turn it right. The position of a closed water supply valve should be horizontal like this:

Water supply valve in closed position

Secondly, open all the hot water fixtures in your house. 

Thirdly, remove the inlet and outlet drain caps on the isolator kits. Then, remove both the drain plugs. Make sure you place a plastic bucket under the drain plugs to collect the residual water. 

Removed the inlet and outlet drain caps on the isolator kits

Now, remove the water drain valve filter out of the inlet. 

Water Drain Valve Filter On Noritz Water Heater

Next, clean the filter with a brush under running water. In this way, you can remove debris and sediments from the filter evenly. 

Cleaning the filter under running water

Once you clean the filter thoroughly, let it dry. You can also towel-dry the water drain valve filter. 

Fourthly, reinsert the water drain valve filter into its place and close the drain plugs. Also, don’t forget to close all the hot fixtures in your house. 

Finally, turn on the water supply valve to verify no water is leaking out of the drain plugs or the drain valve. 


Why is my tankless water heater not heating water?

Your tankless water heater won’t heat the water due to the following reasons:

  • No water and gas is supplying to the unit
  • Electrical issues
  • Feed your tankless unit with improper gas type
  • Gas pressure is not within specs
  • Air in the gas line 
  • Cross plumbing
  • The heat exchanger gets clogged by sediment buildups 
  • Error codes displayed

How do I reset my Noritz tankless water heater?

It’s simple. Just unplug the power cord from the electrical outlet, wait 30 minutes, and re-plug it. It will reset your Noritz Tankless Unit. I also wrote an article on this topic, which you can check out here

What would cause a tankless water heater to go cold?

Several reasons are responsible for a tankless water heater to go cold, including:

  • Cross plumbing
  • Water pressure goes low
  • Dirty heat exchanger
  • The water heater doesn’t meet your daily water usage or demand
  • Size the gas line incorrectly 
  • Cold water sandwich effect 
  • The water filter gets clogged by sediments


Nobody wants to freeze his comfort-feeling in a chilly day of winter. So, it’s a must to fix the water heater issue to enjoy the comfort of hot water. 

If your Noritz Tankless Water Heater delivers no hot water, I recommend you resolve the five common issues I mentioned. I hope you can fix the problem by following those troubleshooting steps. 

However, don’t hesitate to call a plumber if those solutions I offered bring no luck for you. Happy Plumbing!

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