Navien Tankless Water Heater Post Purge

Navien Tankless Water Heater Post Purge

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

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.

Pump Post Purge Time

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. 


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. 

Read Also:

Navien tankless water heater standby mode

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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?

    1. It’s normal as the goal of post purge operation is to throw away unburned gas from the ignition chamber.

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