Noritz Tankless Water Heater Won't Turn On

Noritz Tankless Water Heater Won’t Turn On [5 Easy Solutions]

Noritz Tankless Water Heater won’t turn on due to:

  • Too low water flow rate
  • Insufficient electric supply
  • Gas supply problems
  • A tripped circuit breaker
  • The vent gets clogged

Throughout this troubleshooting guide, I will break down each of those culprits. So, stay in tune till the end to turn the unit on again to get the comfy hot water. 

Table of Contents

Noritz Tankless Water Heater Won’t Turn On [5 Easy Solutions]

This chapter will disclose the culprits that cause the unit to not turn on. 

1. Water Flow Rate Is Too Low

Low water flow rate is the number one reason that prevents the unit from turning on. 

Every tankless water heater has a minimum water flow rate to activate the unit. And your Noritz Water Heater is not an exception to that. The minimum water heater flow rate for operation is 0.5 GPM. If the water flow through the unit is less than that minimum flow rate, the unit won’t turn on. 

Several reasons are to blame behind low water flow, including: 

  • A clogged water drain valve filter
  • The flow sensor gets damaged
  • Cross plumbing 
  • Low water pressure 

How To Fix: 

If the water drain valve filter gets clogged by debris or sediments, the hot water will never run smoothly through the unit. To avoid this situation, you should clean the water drain valve filter. To learn how to clean this filter, check this article on Noritz Tankless Water Heater Maintenance.

Next, inspect the flow sensor and replace it if you observe damaging signs like cracks on it. 

Cross plumbing can also be responsible for low water flow rate. Check the plumbing and ensure you plumb the hot water and cold water lines in a sequence. 

Nonetheless, low water pressure can affect the flow of water that goes through the unit. A closed or partially opened shut-off valve for water, sediment buildup in the heat exchanger, and high-demand some culprits that affect both the water pressure and the flow rate. 

To fix these issues, check the shut-off valve for water. Ensure you fully open the shut-off valve so that the water can flow trouble-freely. Next, inspect the heat exchanger for blockage and descale the unit. If you don’t know how to descale the unit, you can read this guide

Lastly, don’t use too much hot water so that it crosses the heater demands.

2. Insufficient Electric Supply

The tankless water heater from Noritz requires 120VAC (at 60Hz) of electric supply for proper operation. 

If the unit doesn’t get that amount of electric power, the water heater won’t turn on. Wiring issues can cause the water heater to not get enough electric power. 

Turns out, if the electric outlet you use to plug the unit is not functional, you will never get sufficient electric supply to the unit. 

Using an inappropriate circuit is also responsible for getting insufficient electric power to turn on the water heater.  

How To Fix: 

To begin with, I earnestly recommend you to call a certified electrician if you don’t get enough electric supply. Let the service guy fix the issue behind this. 

In addition, ensure the electrical outlet you use to connect the water heater is functional. You can easily verify whether the outlet is working or not by plugging in other appliances like the phone charger. 

And last not the least, make sure you use an inappropriate circuit, whose power consumption will be up to 306W or higher if you use optional accessories. 

3. Gas Supply Issue

You can’t turn on your Noritz Tankless Water Heater if you don’t have sufficient gas supply at the unit. The gas supply at the unit will be interrupted if you don’t fully open the gas valve. 

Besides, sizing the gas meter improperly for the water heater and other  gas appliances can affect the gas supply at the unit. 

How To Fix: 

First off, check the gas valve position on the water heater. If the gas valve is at the off position, turn it counterclockwise to let the gas flow freely. The gas valve should be parallel to the piping if it’s On. 

Next, you must size up the gas meter properly for the water heater and other gas appliances for operation. Install a gas meter that could supply the entire BTU for every gas appliance in the building. 

Also, don’t forget to feed the water heater with the proper type of gas. In this case, check the water heater rating plate and see what type of gas it requires for combustion. 

4. Circuit Breaker Gets Tripped

A circuit breaker for the water heater may get tripped for several reasons. 

For instance, a short circuit in the wire lines, water heater produces excessive temperature, and malfunctioning breaker are responsible for the breaker to go trip. 

When the unit gets tripped, you can’t turn on your Noritz Water Heater. 

How To Fix: 

For short circuits in the wire lines, I highly recommend you to call a certified electrician to deal with this issue. 

Secondly, overheating can also cause the unit to trip the breaker. Several reasons are responsible for an overheated uni. And a clogged heat exchanger is the leading culprit behind this issue. In this case, flushing the unit will help you fix this issue. 

Lastly, the circuit breaker for the water heater is itself at fault. Regarding this, you must replace the circuit breaker to operate the unit properly. 

5. Blockage in the Vent

If you want the Noritz water heater to heat water properly, the exhaust vent should be free from blockage. Otherwise, it will affect the normal operation of the water heater. In the worst case, you can’t even turn on the unit. 

How To Fix:

Just clean the exhaust vent and walk away. You can run a vent cleaning tool to turn it through the vent pipe to release blockage. Either way, you can take apart each venting section to clean the venting with ease. 

How To Turn On Noritz Tankless Water Heater?

Turning on a Noritz Tankless Water Heater is simple as you open the hot fixtures. Just follow the below 4 steps to turn the unit on: 

  • Turn on the water supply valve. When the water supply valve is on, it should be parallel to the piping.
  • Open  a hot water faucet to verify water is available. Then, close the faucet again.
  • Open the gas supply valve. The position of this valve should also be parallel to the supply line. 
  • Turn on the power. 

How Do You Reset A Noritz Tankless Water Heater?

It will come handy to learn how to reset the Noritz Water Heater. As a result, you can reset an error code and let the unit work smoothly. 

To reset the Noritz Water Heater, just unplug the water heater from the electric connection. Then, wait 30 seconds. Lastly, plug the unit into the electrical outlet and press the power button, which will reset the water heater. 

You can also reset the unit with the help of the circuit breaker. To learn more, check this article on Noritz Tankless Water Heater Reset Button


Never expect the water heater to deliver hot water when you can’t turn the unit on. 

I mentioned all the culprits like low water flow, insufficient electric supply, and gas supply issues that prevent the unit from turning on. Luckily, I also described the solution to those problems. 

What you need to do now is just walk through the troubleshooting step and fix those. 

Apart from these, the bonus point for you is to protect the unit from freezing if you live in a cold area. Never disconnect the unit from electric connection as it deactivates the freezing protection feature. 

Good Luck!

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