Navien Tankless Water Heater Post Purge

What Is Post Purge On Navien Tankless Water Heater?

This is a complete guide on Navien Tankless Water Heater Post Purge. From this guide, what you are going to learn: 

  • What is post purge? 
  • How to change post purge time
  • Difference between pre-purge and post-purge
  • How to bleed air on Navien Tankless Water Heater?

So, let’s get started right here. 

Table of Contents

What Is Post Purge On a Navien Tankless Water Heater?

Post-purge on the Navien Tankless Water Heater indicates the cycle that comes at the end of the burner cycle to purge the air out of the combustion chamber before the fan shuts off. 

Actually, you should perform the post-purge after shutting down your water heater. The purpose of post-purge is to remove any unburnt fuel from the ignition chamber and make the unit ready for the next sequence  of ignition. 

Generally, you can control the post-purge by a push of the button. However, some water heaters come with factory set pre and post purge timing. On Navien Tankless Water Heater, you can set the pre and the post purge timing between 0-120 seconds. 

In the next chapter, I will discuss the post purge time. So, keep scrolling.

How To Change Post-Purge Time On Navien?

You can use this function to set the post purge time after a combustion cycle is completed. Here how you can change the post purge time: 

  • Access the Parameter information mode and use the Up or the Down button to select P.06 from there. 
  • Enter the pump post purge time by pressing the Info button. 
  • Once you enter the pump post purge time, it’s time to adjust the post purge timing. Regarding this, press either the Up or the Down button to adjust the valve. 
  • Finally, press the Info button to finalize your desired value.  

Difference Between Pre-Purge and Post-Purge On Water Heater

Pre-purge, as the name suggests, is the cycle that should be done before ignition. In other words, it’s the cycle the burner goes through before it lights up to ensure safety and purge out the combustion chamber. 

On the other hand, the post-purge is done after shutting the unit down. 

The goal of pre-purge the burner is to remove any residual fuel vapor from the combustion chamber for safe and complete ignition. In contrast, the post-purge helps to remove the unburnt fuel from the combustion chamber to prepare the unit for the next usage.  

Yes, pre-purge and post-purge are different. But both of them ensure safety ignition or water heater operation. Both involve blowing air through the combustion chamber with the fuel shut-off. 

How To Bleed Navien Tankless Water Heater?

Air Bleeder Valve On Navien Water Heater
Air Bleeder Valve On Navien Water Heater

To bleed air out of your Navien Tankless Water Heater, follow these five steps: 

  • Turn the power off to your water heater at the circuit breaker.
  • Locate the air bleeder or pressure relief valve at the bottom of the unit.
  • Turn the valve counterclockwise to bleed air or pressure out of your Navien Tankless Water Heater. When you turn on the valve, water will come out, which indicates the pressure or air is released. 
  • Close the air bleeder valve by turning it clockwise.
  • Restore the power of your water heater. 


What Does DHW Mean On Navien?

DHW or Domestic Hot Water on Navien means the unit switches from space heating to DHW mode. It means the unit uses its full capacity to heat the water until the demand stops, providing an endless hot water supply.

Why Does My Navien Water Heater Say Standby?

Navien Tankless Water Heater Standby Mode indicates that either the hot water usage demand exceeds or there is no demand for hot water for an extended period. Your Navien Tankless Water Heater goes into standby mode for several reasons, including no hot water demand, excessive hot water demand, or high-temperature setting.

How To Reset Navien Tankless Water Heater?

To reset your Navien Tankless Water Heater, follow these steps: 

  • Turn the power off of the unit and shut off the cold water supply.
  • Locate the reset button labeled as the Back button on the front control panel.
  • Press the reset button. 
  • Wait for several seconds
  • Restore the power, turn on the cold water supply, and turn on the unit.


You must set the post purge system on your Navien Tankless Water Heater. It helps to remove unburnt fuel from the ignition chamber or the heat exchangers. As a result, you will get the unit ready and safe for the next sequence of ignition. 

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  1. I can smell gas (faintly) after the the post purge operation on my outdoor Navien heater. So that is normal and nothing to be concerned since it is flushing out unburned fuel?

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