fixing common problem with navien tankless water heater

Navien Tankless Water Heater Troubleshooting: A Complete Guide

Having a problem with your Navien tankless water heater, or do you just want to be aware of those common problems with the brand before you buy it? Whatever the reason, we have got you covered, so keep reading!

Navien tankless water heaters are a popular choice for homeowners thanks to their energy efficiency and endless hot water supply. However, like any appliance, they can experience issues from time to time. That’s why we’ve put together this comprehensive guide to help you troubleshoot common problems and keep your Navien tankless water heater running smoothly.

This guide covers everything from flow sensor issues to control board failures and error codes. You will learn how to fix those to get that hot water flowing back in no time and save money and time in the process. So let’s get started!

A. Functional problems with Navien tankless water heater

In this part, we will cover issues like water not heating, low flow rate, or very hot water.

1. Cold water or no hot water!


No hot water is when cold water comes from hot water taps, showers and less hot water than it used to be. There are several potential causes of no hot water, including a malfunctioning water heater, a broken hot water pipe, an issue with the hot water delivery system, or a problem with the hot water valve. In some cases, the fault may be with the electrical or gas supply to the water heater.

Fixing the cold water

To fix the problem of no hot water, you will need to determine the cause. Here are some steps you can take to diagnose and fix the problem:

  • Check the thermostat on the water heater to ensure it is set to the correct temperature.
  • Make sure the water heater is receiving the correct electrical or gas supply.
  • Check the hot water delivery system to ensure no leaks or clogs in the pipes.
  • If the problem is due to a malfunctioning water heater, you may need to have it repaired or replaced.
  • If the problem is due to a broken hot water pipe, you will need to have it repaired or replaced.
  • If the problem is due to a problem with the hot water valve, you can fix it by replacing it.
  • Hearing strange sounds or haven’t flushed the heater for a year or more? It’s time to do it now.

2. Water is too hot

setting water temperature in tankless water heater

If you have noticed that the water coming from your taps or shower is too hot, it can be a sign of an issue with your hot water system. The most common cause of this problem is a malfunctioning thermostat or a misadjusted temperature control. The thermostat is responsible for regulating the water’s temperature and ensuring it stays within a safe range. If it’s not functioning correctly, the water can become too hot. This guide will help you text and fix the thermostat.

You may also notice that your hot water system is making strange noises or that the water temperature is inconsistent between different fixtures.

Fixing too hot water

Here are some steps you can take to fix the problem:

  • Adjust the temperature control: If you have a temperature control knob or dial, you can try adjusting it to see if that fixes the problem. Be careful not to set the temperature too high, as this can be dangerous.
  • Check the thermostat: If adjusting the temperature control doesn’t solve the problem, you can check the thermostat to ensure it’s functioning correctly. If the thermostat is faulty, you will need to replace it.
  • Flush the heat exchanger: Scales and hard water buildup make the water heater work inefficiently. If you haven’t flushed or descaled your water heater for years, it’s time to see if this fixes the issue or call a plumber. This complete guide to descaling water heater will come handy.

3. Navien is constantly running

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Navien tankless water heater range. Credit: Navieninc

A Navien tankless water heater is designed to heat water on demand, so it should only run when a hot water tap is turned on. However, if your tankless water heater is constantly running, it is continuously heating water even when no taps are open. 

This can be caused by various factors, including a leaking hot water tap, a faulty thermostat, a clogged air filter, or a malfunctioning igniter.

Symptoms of constantly running tankless water heaters

  • Hearing the constant water heating or appliance operating sound from within. 
  • Higher than usual and unexplained energy bill, as the water heater uses more energy than necessary.

Fixing constant running Navien tankless water heaters

To fix constant running in a Navien tankless water heater, you may need to troubleshoot and replace one or more parts of the system. Here are some steps you can take to diagnose and fix the problem:

  • Check for open or leaking hot taps: Go and check all those taps across your house for leaking, dripping or open taps. They may be keeping the heater running all this time. 
  • Check the thermostat: If the thermostat is not functioning correctly, it may be causing the water heater to continuously heat water. You can test the thermostat by turning the temperature control dial down to a lower setting and observing whether the water heater stops running. If the water heater continues to run, you may need to replace the thermostat.

4. Strange noises from the heater

A tankless water heater is supposed to operate quietly, so any unusual noises you hear from the unit can indicate an issue with the system. These sounds can range from a low hum to a high-pitched whine, and they can be unsettling, to say the least. You may also hear banging, rattling, and whistling. Each of these noises could indicate a different problem, so you must listen closely and determine what type of noise you’re hearing.

Some common causes of strange noises in Navien tankless water heaters include scale and lime buildup in the heat exchanger or water lines, loose or damaged parts, blocked vents, and issues with the circulation pump.

Fixing the strange noises

First, you’ll need to determine the source of the problem. 

  • If you suspect that mineral buildup is the issue, you can try flushing the water heater to remove any buildup. 
  • You can inspect the system and tighten any loose connections if there are loose parts. 
  • For malfunctioning components, you may need to repair or replace them.

B. Technical problems with Navien tankless water heater

Here we have discussed more mechanical and complicated issues with the appliance, like parts failure, error codes, and electrical issues.

5. Flow sensor issues

A flow sensor is a device that measures the flow rate of water in a tankless water heater. It signals the heating unit to activate and produce hot water when a faucet is turned on, and it also helps regulate the temperature of the water. The flow sensor ensures that the water heater operates efficiently and provides hot water as needed.

Symptoms of a faulty flow sensor

If your Navien tankless water heater is experiencing flow sensor issues, you may experience one or more of the following symptoms:

  1. No hot water: If the flow sensor is not functioning correctly, the heating unit may not receive the signal to turn on, leaving you with cold water.
  2. Inconsistent water temperature: Faulty flow sensor may not accurately measure the water flow rate, and the water temperature may be inconsistent. This can result in scalding hot water at times and lukewarm water at others.
  3. Error codes: Navien tankless water heaters are equipped with error codes that help diagnose problems. If the flow sensor is malfunctioning, you may see an error code indicating a problem with the flow sensor. Commonly it shows ERROR 001, ERROR 038, or ERROR 039 for flow sensor issues.

Fixing faulty flow sensor

If you suspect your Navien tankless water heater is experiencing flow sensor issues, there are a few steps you can take to try and fix the problem:

  • Clean the flow sensor: If the flow sensor is dirty or clogged, it may not be able to accurately measure the water flow rate. Clean the flow sensor with a soft cloth and check for any obstructions.
  • Check the water flow rate: Ensure the flow rate is within the recommended range for your Navien tankless water heater. If the flow rate is too low, it may not be able to activate the heating unit.
  • Replace the flow sensor: If cleaning and adjusting the water flow rate doesn’t solve the problem, it may be necessary to replace it. A professional plumber should perform this task to ensure the proper installation and functioning of the new flow sensor.

6. Control board failure

Navien Tankless Water Heater control board.
Navien Tankless Water Heater control board. Credits; MHG

The control board is the computer, the brain of the tankless water heater. It plays an essential role in controlling all its functions. When the control board fails, it can cause severe problems with the tankless water heater and affect its performance. Here are the symptoms of a control board problem and the solutions for fixing it.

Symptoms of a control board problem

  1. No hot water: If you don’t have any hot water coming out of your faucets, it could be a problem with the control board.
  2. Error codes: You may see an error code like “E015”, which means a control board issue.
  3. Unexpected shut-off: If your tankless water heater suddenly shuts off for no apparent reason, it could be a problem with the control board.

Fixing control board failures

  1. Checking the wiring: One of the first things you should check when encountering a control board issue is the wiring. Check if the wiring is securely connected and if there are no signs of damage or corrosion.
  2. Checking the electrical connections: The control board is powered by electricity, so it’s essential to check the electrical connections to make sure they’re working correctly.
  3. Replacing the control board if necessary: If the above steps don’t solve the problem, you may need to replace the control board. It’s a complex process and should be done by a professional to ensure it’s done correctly.

7. Cracked heat exchanger

fixing common problem with navien tankless water heater

It’s the heart and soul of a tankless water heater. As the name suggests, a heat exchanger transfers heat from the combustion process to the water flowing through the unit. It ensures that the water is heated efficiently and quickly, providing a steady hot water supply whenever needed. One of the most common problems with a heat exchanger is cracking.

Symptoms of a cracked heat exchanger

  1. No hot water: Common symptom with other problems. If the heat exchanger is cracked, it may not be able to transfer heat to the water efficiently, resulting in a lack of hot water.
  2. Water leakage: If the heat exchanger is cracked, water can leak out of the unit, causing water waste and floor damage and reducing the tankless water heater’s efficiency.

Fixing a cracked heat exchanger

  • Identifying the source of the crack: The first step in fixing a cracked heat exchanger is to identify the source of the crack. This may involve disassembling the unit and examining the heat exchanger for signs of damage.
  • Repairing or replacing the heat exchanger: If the crack is small and does not affect the structural integrity of the heat exchanger, it may be possible to repair the crack. However, if the crack is beyond repair, you will want to replace the entire component or heater.

8. Navien Error codes

Navien Tankless Water Heater Troubleshooting and Error Code Definitions
Navien Error Code. Credit: SEP

Navien tankless water heaters are high-tech and flash trouble codes when there’s any problem detected with the system. These are displayed on the appliance’s control panel and indicate a specific issue that needs to be addressed. This code helps homeowners with fixing the problem. So obviously, understanding these codes will save you time and energy by helping you effectively resolve it.

List of common error codes and their meanings

Here are some of the most common error codes that can appear on a Navien tankless water heater and their meanings:

  • E003: Ignition failure. This error code indicates that the ignition system has failed and there is no gas or insufficient gas supply. Other potential causes include a defective flame rod and a bad PC board.
  • E004: False flame detection. It may also mean that the electrical cord isn’t properly grounded.
  • E012: Flame loss. This error code can occur because of dirty air intake filters, or the unit plugged into a poorly grounded outlet.
  • E047: Exhaust thermostat abnormality. The interpretation here is that the exhaust thermostat is behaving abnormally.

Resolving error codes

If you are experiencing any of the above error codes, here are some fixes you can try:

  • Check the water flow rate: If the water flow rate is too low, the tankless water heater will shut down. Ensure that the water flow rate is within the recommended range.
  • Check the electrical connections: Make sure that the electrical connections are tight and secure. If the electrical cord isn’t properly grounded, this can cause false flame detection.
  • Reset the breaker: If the unit trips, reset it and try rerunning it.

9. Bad pressure valve


The pressure valve is designed to maintain a safe operating pressure within the system. The valve acts as a safety release mechanism that opens when the pressure inside the water heater exceeds a predetermined level. Over time, the pressure valve can become worn or damaged, leading to a breakdown.

Several factors can contribute to pressure valve failure apart from wear and tear, including hard water buildup, improper installation, high pressure etc. [ If you have low pressure then refer to this guide.]

Symptoms of broken pressure valve or issue with it

When the pressure valve in a Navien water heater breaks or malfunctions, it can cause several symptoms, including:

  • No hot water: If the pressure valve is stuck in the closed position, it can prevent hot water from flowing into the system.
  • Leaking water: If the pressure valve is stuck in the open position, water may leak from the valve, indicating a problem. You will see a puddle underneath your heater.
  • Noisy operation: A malfunctioning pressure valve can cause excessive noise and vibration within the water heater.
  • High water pressure: If the pressure valve is not functioning properly, it can lead to excessive water pressure within the system, which can cause damage to pipes, fittings, and other components.

Fixing bad pressure valve

There are several steps you can take to try to fix the issue:

  • Check the water pressure: If the water pressure is too high, this could cause a problem. Adjust the water pressure to the recommended level and see if this resolves the issue.
  • Clean the valve: If mineral buildup is affecting the operation of the valve, try cleaning it with a solution of white vinegar and water. Let the solution soak in for several hours, then flush the valve with clean water.
  • Replace the valve: If the pressure valve is damaged beyond repair, it will need to be replaced. This is a job that is best left to a professional plumber.
  • Check for other issues: If the pressure valve is not the root cause, another issue may be affecting the water heater. Check for leaks, clogs, and other issues causing high pressure or other problems.

10. Tripped breaker

fixing tripped breakers

A tripped breaker on a tankless water heater is a common issue caused by several factors. The breaker is designed to trip and shut off the power to the water heater if it senses an electrical problem, such as an overloading or short circuit. 

Symptoms of a tripped breaker

  • The obvious one is tripped breakers in the breaker panel for the heater.
  • With tripped breaker and no power to the appliance, you will see water not heating. 
  • It may flash relevant error codes.

Fixing tripped tankless water heater breaker

  1. Check the wiring: Check all the wiring connected to the water heater, including the power cord, to ensure that there are no loose or frayed wires.
  2. Check the electrical connections: Ensure that all the electrical connections to the water heater are secure and not loose.
  3. Reset the breaker: Locate the breaker that controls the power to the water heater and reset it. To reset the breaker, turn the switch to the off position, wait a few seconds, and then turn it back to the on position.

You should be aware that working with electricity can be dangerous, and you should seek the help of a professional if you are unsure about the electrical connections or are not experienced in electrical work.

Over to you!

In conclusion, Navien tankless water heaters are reliable and efficient. Still, the electric appliance is prone to issues such as a clogged air filter, faulty ignition, and fluctuating temperature. 

Regular maintenance, which includes flushing the system and replacing the air filter, can help prevent these problems. If you encounter more severe issues with your tankless water heater, it is recommended to seek professional assistance to avoid causing further damage. 

I hope this guide answered all your questions and helped fix the trouble with your Navien water heater. If you are still having a problem that won’t fix, then don’t forget to ask us in the comment below and don’t forget to take the help of a professional.

FAQs related to Navien tankless water heater

1 What is the life expectancy of a Navien tankless water heater?

The life expectancy of a Navien tankless water heater is estimated to be 15 to 20 years, with the potential to last even longer with proper maintenance.

The length of the service life of a Navien tankless water heater can be influenced by factors such as water quality and usage, as well as proper maintenance. Navien offers a 15-year warranty on their tankless water heaters, which covers the dual stainless steel heat exchangers.

2 Is Navien’s tankless water heater a good brand?

Navien is one of the best brands for tankless water heaters, known for their high-efficiency heat exchangers that last for years without breaking down. You can expect Navien models to last for 15-20+ years with proper and regular maintenance.

3 How often should you flush a Navien tankless water heater?

It is recommended to flush a Navien tankless water heater once a year to maintain its performance and longevity. During the flush, any accumulated minerals or sediment in the unit are cleared out, ensuring that the water heater continues operating optimally. 

Regular maintenance, such as flushing, can also help prevent potential problems and extend the unit’s life.

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