Navien Tankless Water Heater Won’t Turn On [5 Easy Fixes]

The main reasons behind Navien tankless water heater won’t turn on are electrical issues, no fuel source, and no ignition. Besides that, flame failure and a faulty control board can also cause this problem.

navien tankless water heater won't turn on

You can solve this problem in most cases by refilling your gas tank, turning on the gas valve, and fixing the electrical issues.

However, that doesn’t mean you should ignore the other reasons behind your heater not turning on as they’re also quite common. Keep reading to find out all about them and how you can fix them in detail. Let’s dive in!

Table of Contents

We’ll discuss the most common causes behind Navien tankless water heater won’t power on and how you can solve them in this section.

1. Electrical Issues

Even if your Navien tankless water heater is operated by gas, it still needs electrical power to turn on. If there are any issues with the electrical system in your house, it could be why your Navien water heater won’t turn on.

electrical issues

Here are the main things that could go wrong with your electrical system that you should start checking immediately:

  • A blown fuse.
  • The circuit breakers can get tripped.
  • The electrical power outlet is in horrible shape and malfunctioning.
  • Faulty power cable.


If you find that you’re facing any of these issues when diagnosing it, here’s how you can go about fixing them:

Blown Fuse– If you find a blown fuse in the electrical system that supplies power to the heater, you need to replace it.

Tripped Circuit Breakers– You can simply switch the circuit breaker to the “On” position if it has been reset. When a breaker has been reset, it won’t be in the “Off” position and you’ll find it stuck in the middle.

It indicates a deeper problem with the electrical system in your house. You should check it by a certified electrician.

Bad Power Outlet– Your water heater needs to be connected to a properly grounded electrical outlet. Make sure the one you’re using is a 120VAC electric outlet. If it’s in bad shape and not working anymore, you’ll have to replace it with a new one.

Faulty Power Cable – If the plug or cable of your water has gone bad, you’ll have to replace it as well to get your heater to turn on.

2. No Fuel Source

Another common reason behind your Navien tankless water heater not turning on is having an empty gas tank. Your heater needs gas to operate and heat the water. Otherwise, you won’t get any hot water from it.

navien tankless water heater empty gas tank

So, inspect your gas tank and make sure that there’s a sufficient amount of gas in it. If you have gas, the next thing you must ensure is that the main gas valve is not turned off. 

main gas valve is not turned off


These are the easy fixes you can follow to get your Navien tankless water heater up and running again:

  • If you’re running low on gas or have an empty tank, you need to refill it.
  • Turn on the gas valve if it’s off.

3. No Ignition

You’ll face the Navien tankless water heater with no power issues when there’s ignition failure. The most common indicator of ignition failure is seeing the E003 error code in your water heater.

ignition failure is seeing the E003 error code

The main reasons behind it are supply issues with the gas. Since you’ve already ensured that the main gas valve is on and you have sufficient gas, the next thing to check is the gas line size.

You also need to use the right type of fuel that’s required by your heater. Using natural gas in a propane heater won’t work properly. Here are the ideal gas pressures you’ll need to maintain to ignite the water heater:

Type Of GasLowest Gas PressureHighest Gas Pressure
Natural Gas3.5 in W/C10.5 in W/C
Propane (LPG)8 in W/C13 in W/C

You have to change the gas line to a larger size when you install a tankless water heater. While normal gas lines are 3/4th of an inch, it needs to be 1/2″ to 1″ in diameter.

If you’ve installed the heater yourself, it’s likely that you didn’t change the size of the gas line.


Make sure that you’ve paid the gas bills and that there are no leaks in the gas lines. Upgrade the gas lines to the recommended size to make sure there’s enough gas pressure. Doing these things should solve the gas supply issues and use your heater without any difficulty.

4. Flame Failure

If your Navien tankless water heater won’t stay on, flame failure is a potential reason behind it. You’ll usually get a message indicating “Flame Failure” in the display of your heater when it happens.

navien tankless water heater won't stay on

It indicates that something is keeping your heater from staying ablaze. Gas supply issues can cause this problem. Hopefully, you’ve checked and fixed those issues by now.

Besides the gas supply problems, blocked vents can also cause this problem. Inspect the vents connected to the heater and see if you can find any blockage. While you’re at it, check if you can find any holes in the pipes.

blocked vent pipe


Here are the fixes you can do depending on the problem you were facing:

  • If you find birds or rodents taking up space in your vents, move them from the area.
  • Clean any other visible blockage you can see that can cause this issue.
  • Replace the pipes altogether if you find any holes in them.

5. Faulty Control Board

Still, wondering why won’t my tankless water heater turns on. The Navien control boards can fail from time to time, especially, if they’re old and have been used for a long period. There could be many symptoms that could indicate this issue.

navien tankless water heater faulty control board

The most common one is that your heater will turn on, off, and on again repeatedly on its own. A damaged control board can also falsely trigger the E003 error code that indicates ignition failure.


Although the symptoms of a bad control board are hard to narrow down, you can try a quick solution first if you saw any of the signs listed above. Unplug the heater and plug it in again to see if it solves the issue for a while.

If that works in the short run, that means you’ll have to eventually replace the control board for a permanent solution to this problem. It can cost anywhere between $150 – $300 to get a new PCB for your heater.

You can easily replace it on your own if you’re good at using some basic tools for housework. Make sure you get the right part number as there are a few different styles of control boards available.

With that said, here are the steps you can follow in order to replace the control board in your Navien water heater:

Step 01 – Remove The Display Module

  • Shut off the water supply and turn off the power of the heater.
  • Remove the front cover and take a picture of the wire connections so that you can put them back correctly later on.
  • Take off the display module in front of the board.

Step 02 – Remove The Old Control Board

  • Remove the three screws holding the motherboard in place. One of them will be located at the top side and the remaining two will be at the bottom.
  • Take a picture of the control board again and make sure you keep note of which wire goes into which slot.
  • Disconnect the wiring harnesses and remove the control board.

Step 03 – Place The New Control board

  • Put the new control board in place of the old one.
  • Use the pictures or notes you gathered to make sure you place all the wires in the correct spots.
  • Tighten the screws to secure the board in place and install the front cover.

That’s how you can replace the motherboard yourself following some easy steps. If you’re not comfortable doing it yourself, you can always contact Navien customer support to do it for you.


How to reset Navien tankless water heater?

Just press the reset button on the front panel of your Navien tankless water heater and the unit will reset on its own.

Where is the reset button on a Navien tankless water heater?

The reset button is located right in the front panel along with the other buttons to turn on the heater and change the temperature. 

How to turn on Navien tankless water heater?

You can turn it on by simply pressing the power button located in the front panel. Try resetting the heater if you see any error message and see if that solves the problem before taking further steps.

How often should Navien tankless water heaters be serviced?

Navien water heaters generally last for a long time. You can easily use them for more than 20 years if you do annual maintenance of them.

What is Navien tankless water heater standby mode?

The standby mode is a safety feature that keeps the heater from working when you’re using too much hot water or the temperature exceeds safe levels. You can reset the unit to get out of this mode.


Cold weather is bad by itself and it’s comforting to know that you can at least enjoy a hot shower and relax. But when your Navien tankless water heater won’t turn on, it can get extremely frustrating.

At least now you know what causes this issue and how you can fix it after completing this guide.

Comment below on what was keeping your Navien heater from working and how you fixed it. Feel free to ask any questions about Navien tankless water heaters.

Note: You can also read how to fix navien tankless water heater temperature swings problems.

About David

David is a man who loves doing research and finding out the best solution to any type of heating appliance issues like heaters and fireplaces. Whenever he finds the perfect solutions to any issues of heating appliances after doing in-depth research, he loves to share them with his readers. In fact, his aim is to help his readers to fix the issues with their heating appliances easily.More about us .

Leave a Comment