Navien Tankless Water Heater Keeps Turning Off

Navien Tankless Water Heater Keeps Turning Off

Navien Tankless Water Heater keeps turning off if the defective flame rod is at fault or the heat exchanger gets clogged by mineral or scale formation. 

If you want to prevent the unit from shutting down, you must replace the flame rod and flush the heat exchanger. 

Apart from these, gas flow issues, tripped high limit switch, and bad controller are other culprits that will cause the unit to go off. 

And this troubleshooting guide will describe every troubleshooting step to fix the turning-off issue. So, read between the lines till the end. 

Table of Contents

Why Does My Navien Tankless Water Heater Keep Turning Off?

This chapter will disclose every reason that causes the Navien water heater to keep turning off. Plus, you can learn how to resolve those issues. 

01. Defective Flame Rod

A faulty flame rod or igniter is the first component I suspect if your tankless water heater keeps turning. 

Generally, the flame rod igniter senses the flame and sends a signal to the PCB to let the unit call for heat. If the flame rod is at fault, it won’t sense the flame and provide no signal to the controller. As a result, your water heater will go off. 

To bring the unit back into normal operating state, you must replace the faulty flame rod. 

How  To Fix: 

Replacing the flame rod requires you to remove the front panel. First off, turn off the water heater. Then, unscrew the front panel cover and remove it. Next, locate the flame rod, which you can find below the blower fan.

Before removing the blower fan, ensure you disconnect the flame rod wire connector. 

Now, unscrew the nuts that hold the blower fan in place and pull it out.  Afterward, remove the nut that holds the flame rod in place and remove the flame rod. If the rod gets burnt out, replace it with a new one. 

Don’t forget to check the condition of the flame rod wiring. If it gets pinched or damaged, replace the wiring as well. 

Once you replace the flame rod, secure it with the nut. Then, reconnect the flame rod connector. Finally, secure the blower fan with the nuts, replace the front panel cover, and turn on the unit. 

02. Clogged Heat Exchanger

When is the last time you flush your tankless water heater? For proper water heater operation, you should flush the unit once a year. However, it requires you to flush the unit every six months if you live in a hard water heater. 

If you don’t flush the unit routinely, mineral deposits or scale formation will clog the heat exchanger. This scale formation causes the heat exchanger to get overheated and turn the water heater off. 

How To Fix: 

Flush your water heater according to the manufacturer guideline. It will help remove all the mineral deposits from the heat exchanger to operate the unit smoothly. To flush the unit, you should have the following pieces of equipment at your fingertips: 

  • A 5-gallon capacity plastic bucket
  • Two hoses
  • Cleaning solution
  • And a circulation pump

After having these flushing kits, follow the flushing steps described in this article on Navien Tankless Water Heater Maintenance

03. Problem With Gas Flow

Your Navien water heater requires a continuous flow of gas to operate the unit. If it doesn’t get a sufficient amount of fuel, you will never turn on the unit. Generally, your water heater will not receive any gas due to the following reasons: 

  • Gas control valve is not fully open
  • Insufficient gas in the tank
  • No gas flow to the gas meter 

How To Fix: 

First off, ensure the gas control valve is in the On position. If not, turn the main gas control valve counterclockwise. 

Secondly, make sure there is sufficient gas in the tank. If needed, refill the gas tank. 

Lastly, ensure the gas is flowing to the gas meter. I highly recommend you call a qualified plumber if you fail to turn on the unit after trying these troubleshooting steps. 

04. High Limit Switch Gets Tripped

A tripped high limit switch can also cause your Navien tankless water heater to keep turning off. 

The high limit switch is basically a safety feature. When the water temperature of your water heater exceeds the safety level, the high limit switch wil cut off the electric supply and turn the unit off automatically. 

Now, the question is- what causes the water temperature to climb up to the safety limit? A dirty heat exchanger is the main culprit behind this issue. 

How  To Fix: 

First off, locate the high limit switch of your Navien tankless unit. If it gets tripped, just reset the switch to the on position. 

On the other hand, if the high limit switch is at fault, you should replace the switch.

And lastly, the suggestion I want to give you is to flush your water heater routinely. Otherwise, the heat exchanger will get clogged by mineral deposits and cause the unit to go off due to overheating. 

05. Bad Controller

A controller or PCB on a tankless unit is known as the brain of the unit. It controls your entire water heater. If the PCB gets faulty, you can’t turn the unit on. 

How To Fix: 

I highly suggest you contact a professional plumber to inspect and replace the bad PCB with a new one. However, you can also do this task yourself if you are mechanically inclined. 


It will be a pain in the butt if the water heater keeps turning off, especially on an ice-cold day of winter. Regarding this, what I recommend you to do is- try to find out the culprit behind this problem. 

Fortunately, I already mentioned all the possible reasons that cause your Navien Tankless Water Heater to turn off. Plus, I also broke down how you can fix the turning-off issue. 

So, follow our troubleshooting guideline to bring the unit back into the normal operating condition.

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