Navien Tankless Water Heater Code E003

How To Fix Navien Tankless Water Heater Code E003?

This is a complete troubleshooting guide on Navien Tankless Water Heater Code E003. What I am going to disclose in this article: 

  • The meaning of error code e003 and what causes the unit to pop up the code
  • How to reset the diagnostic code e003 on Navien Tankless Water Heater?

In short, you can learn how to clear error code E003 and let the water heater ignite & operate flawlessly. 

So, let’s get started. 

Table of Contents

What Is Error Code E003 On Navien Tankless Water Heater?

Error code E003 on Navien tankless water heater means ignition failure. The tankless unit will throw this diagnostic code if the ignition system has failed. Generally, no gas or insufficient gas supply, defective flame rod, and bad PC board are the culprits that cause the unit to pop up the fault code e003. 

Below, I will break down every culprit so that you can clear the error message from the controller display. 

Here we go. 

01. No or Insufficient Gas Supply

No gas will flow to the burner chamber if you don’t fully open the gas control valve. Without fuel, it’s impossible to ignite the unit. Turns out, you need sufficient fuel in the combustion chamber for proper ignition. If there is insufficient gas in the gas tank, the burner will fail to light up the unit. 

How To Fix: 

Start with checking the gas control valve on the unit. Ensure you fully turn the gas valve on to let the gas flow to the combustion chamber. If you don’t turn on the gas control valve, just turn it counterclockwise. 

Next, make sure there is enough gas in the gas tank. If not, refill the gas tank with fuel. 

02. Bad Flame Rod Wiring Or The Flame Rod Itself Is Bad

If the unit gets sufficient fuel for ignition, the next suspicion that causes ignition issues is the bad flame rod wiring or bad flame rod. 

You should remove the front panel and the blower to access the flame rod assembly. So, unscrew the front panel and slide it out. Then, use a screwdriver to unscrew the three nuts that hold the blower in place. Now, hang the blower on a copper hanger and locate the flame rod assembly. 

You can find a thin black wire there, which is the flame rod wiring. It communicates with the PC board and tells the PCB whether there is a flame or not. If this wiring gets damaged or pinched, it won’t send any signal. As a result, the unit throws the error code E003 to let you know there is an ignition issue with the unit. 

Similarly, defective flame rod is responsible for the error code e003. Don’t forget a filthy flame rod can also prevent the unit from igniting and cause the unit to throw the code E003. 

How To Fix: 

Firstly, inspect the wiring to the flame rod. To access the flame rod, remove the front panel and unscrew the blower. Then, visually inspect the flame rod wiring. If it gets damaged, replace the wiring. 

Next, inspect the flame rod and ensure it’s not covered with dirt. If the flame rod is filthy, clean it by gently scrubbing the flame rod with an emery cloth. 

On the other hand, if the wiring is ok and the flame rod is clean, I bet the flame rod is at fault. So, get a new flame rod from Home Depot and replace the old flame rod with a new one. 

03. Bad PC or Motherboard

The PCB or motherboard is the brain of your Navien Tankless Water Heater. It controls the entire unit and its functionalities. If the PC board is at fault, your water heater will display error messages like e003. In short, you can’t ignite the tankless water heater with a bad PCB. 

How To Fix: 

Get a new PCB and replace the old one with it. You can check out this video to learn how to replace the control board on Navien Tankless Water Heater: 

How To Reset The Error Code E003 On Navien Water Heater?

Resetting the error code e003 on the Navien Tankless unit is simple. Just follow the below troubleshooting steps to reset or clear the error message: 

  • Ensure there is sufficient gas in the tank and you turn on the gas control valve.
  • Inspect the flame rod wiring or the flame rod itself. If needed, replace the flame rod or repair its wiring. 
  • Make sure the controller board is fine. 
  • Now, press the back button on the front panel and it will reset the unit & clear the code from the display. 


Ignition failure is a common problem on every tankless water heater. And your Navien tankless unit is not an exception to that. Insufficient gas supply, faulty flame rod wiring or the flame rod itself is bad, and defective PCB are some caveats that cause the unit to flash the error code e003. 

Fortunately, I mentioned every troubleshooting step to fix those issues. So, follow the guideline and service the unit. I hope you can reset and clear the error code e003 from the controller display. 

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