Navien E438 Error Code

Navien E438 Error Code [Solved]

Navien E438 Error Code on the front panel display indicates the recirculation pump is working abnormally. So, what you need to do in this case is- check the recirculation pump and ensure it’s operating properly. 

Apart from this, your Navien tankless unit can also pop up the error message due to a bad check valve or defective flow control sensor. 

Throughout this troubleshooting guide, I will describe every possible reason that can cause your water heater to flash the code E438. So, continue to read. 

Table of Contents

What Does Navien E438 Error Code Mean?

Navien E438 Error Code means the circulation pump is operating abnormally. Several things like a check valve, flow sensor, and pump itself are to blame for a malfunctioning circulation pump. 

I will describe all of these culprits below so that you can understand how they affect the performance of your recirculation pump. 

Here we go.

Check Valve Goes Bad

A check valve on a tankless water heater helps to prevent the backflow of water. This valve will open when the water flows toward the valve and allow the water to flow through it. 

When the water flow stops, the check valve will go into the close position to prevent the water from flowing to the reverse direction.  

If this valve goes bad, water won’t flow through it and reach the recirculation pump. As a result, the recirculation pump will not get enough water flow it requires for functioning. And it causes the unit to throw the error code E438. 

How To Fix: 

Before inspecting the recirculation pump, check the check valve first. So, turn the unit off and remove the front cover panel. Then, locate the check valve, which you can find next to the recirculation pump.  

Inspect the check valve visually to see whether it gets clogged or broken. If it gets damaged, replace the check valve with a new one. The following tutorial will help you change that valve like a pro: 

Bad Flow Control Sensor

A defective flow control sensor is my next suspicion that can cause your Navien water heater to pop up the error code e438. This filter is a small fan-like sensor that spins when the water passes. Over time, it will get covered with scale and mineral deposits and the sensor won’t move anymore. 

How To Fix: 

You should take apart the unit and bring out the flow control sensor from the water heater. Then, clean it. On the other hand, if it gets damaged, you should replace the flow control sensor. You can watch this video to learn how to change the flow sensor: 

Recirculation Pump Itself Is Bad

A defective recirculation pump is the main culprit that causes the unit to throw the fault code e438. If you hear a buzzing noise from the recirculation pump, understand the recirculation pump is working abnormally. 

How  To Fix: 

You should replace the recirculation pump if it functions intermittently. It will be better to call a certified plumber to inspect your water heater. If needed, replace the recirculation pump. 

How To Reset Navien Tankless Water Heater?

Resetting a Navien tankless water heater is a piece of cake. Just locate the Back button on the front panel. This Back button basically works like a reset button on other tankless water heaters. 

So, press the Back button from the front panel and it will reset your Navien water heater successfully. 

Alternatively, you can hard reset the unit. In this case, turn the unit off and unplug the water heater from the electric outlet. Ensure you keep the unit detached from the electric power supply for 30 minutes. 

Then, restore the power supply to your water heater and turn it on, which will reset every setting of your water heater. 


Make sure the recirculation pump is working properly if your Navien water heater throws the error code E438. If the pump is malfunctioning, fix it by replacing the pump. 

On the other hand, if the recirculation pump is functioning, take a look at the check valve or the flow control sensor. If they work intermittently, repair or replace them. 

I hope these troubleshooting steps will help you clear the error code from the display. However, if the error code e438 still persists, call a qualified plumber to deal with this issue. 

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