Nevin tankless water heaters have earned an excellent reputation for their efficiency, durability, and convenience of providing endless hot water when needed. Nevertheless, even the most reliable devices can occasionally experience malfunctions. This comprehensive guide explains common Navien tankless water heater problems and their solutions, empowering you to maintain a constant hot water supply in your home. 

Navien Flow Sensor Problems

1. Pressure Relief Valve Check

One of the most common issues you might encounter with your Navien tankless water heater is the need for hot water. Don’t panic; try a simple fix: open and close the pressure relief valve near the heater’s outlet. This step often resolves the issue and restores your hot water supply.

2. Cleaning the Sensor

In older Navien models, a corroded flow sensor can be the culprit behind heater shutdowns. To address this, To fix this, clean the clamps that are holding the sensor in its spot. However, keep in mind that this problem might reoccur in time. A more long-term solution is to replace the sensor with a corrosion-resistant stainless steel version.

3. Install a Water Inlet Filter

Water impurities can affect the performance of your Navien’s flow sensor. Installing a water inlet filter can help remove these impurities, ensuring your sensor functions optimally.

4. Consider Replacement

If your Navien tankless water heater is getting old and you keep having issues even after trying to fix them, buying a new Navien model might be more convenient. More recent models usually have better features and work more efficiently.

Interpreting Navien Tankless Water Heater Error Codes

Navien tankless water heaters have a helpful error code system to simplify troubleshooting. Here’s a quick guide to standard error codes and their solutions:

1. Error Code E003 – Ignition Failure

If you encounter error code E003, it means there’s an ignition failure. Ensure the main gas supply valve is open to resolve this issue.

2. Error Code E004 – False Flame Detected

For error code E004, check the electrical cord to ensure it is correctly grounded. A secure ground connection is crucial for your heater’s proper functioning.

3. Error Code E012 – Flame Loss

If you encounter error code E012, unplug the unit, remove the intake filter, clean it under running water, allow it to dry, and reinstall it before restarting it. This procedure typically resolves the issue. 

4. Error Code E515 – Unusual Operation of the PCB

Error code E515 indicates an unusual printed circuit board (PCB) operation. Check the electrical cord’s grounding to ensure it’s properly grounded.

5. Error Code E760 – Time to Flush Your Water Heater*

If you encounter error code E760, it’s time to flush your water heater. Refer to your manual for instructions, or contact a plumber for guidance.

For error codes not covered here, it’s advisable to seek assistance from a service technician, as they might indicate more complex issues.

Additional Problems with Your Navien Tankless Water Heater

While less common, older Navien tankless water heater models may experience other issues that require professional guidance. Here are some of these less frequent but critical problems:

1. Cracked Heat Exchanger

A cracked heat exchanger can pose a serious issue, allowing toxic gases to escape. Unfortunately, you cannot repair this. Check your warranty coverage and consider upgrading to a newer Navien tankless water heater if applicable.

2. Control Board Failure

If your Navien tankless water heater cycles on and off without explanation, it could indicate a failing control board. While an error code might display 003, suggesting an igniter malfunction, further investigation may reveal a malfunctioning motherboard. Seek professional evaluation and, if necessary, replacement of the control board.

3. Noisy Unit

Several factors could be at play if your Navien tankless water heater emits unusual sounds. These include loose parts, water line vacuum issues, a defective pressure valve, a dirty flow sensor causing gas flow interference, or a malfunctioning re-circulating pump. To pinpoint and resolve the issue, consult a professional. Ignoring the problem could cancel your coverage if your unit is under warranty.

4. Water Isn’t Staying Hot

A loss of hot water can result from various factors. Here are some of the leading causes and potential solutions:

  • Simultaneous heavy usage: To address this, consider setting up a usage schedule or upgrading to a larger water heater to meet your hot water demands.
  • Low gas supply: If your gas supply is insufficient for your heater’s size, you can resolve this issue by increasing the gas flow to the unit.
  • Damaged flow sensor: A damaged flow sensor can hinder gas flow to the water heater. Contact a professional to inspect and solve this issue.
  • Pilot light won’t stay lit: A pilot light issue could result from a clogged air vent, damaged gas valve, gas supply interruption, dirty burners, or a damaged flow sensor. Cleaning your heater may help, but if the problem persists, seek professional assistance.

5. Tripping Breaker

If your Navien tankless water heater consistently trips the breaker, it’s essential to investigate. While water leaks or wiring issues can be the culprits, electrical problems are more likely. With the breaker in the off position, disconnect the unit and inspect for any signs of leaks. If you don’t find any leaks, disconnect the team and switch the breaker back on. If it remains on, your water heater might be faulty. If it trips again, the problem resides in the electrical system rather than the water heater.


Navien tankless water heaters are renowned for their reliability, efficiency, and long service life. However, as with any appliance, occasional issues can arise. Following the troubleshooting steps outlined in this guide can effectively address common problems and ensure a continuous hot water supply in your home. For more complex issues or when in doubt, always consult a professional plumber or technician for expert assistance. With the proper guidance and maintenance, your Navien tankless water heater can continue serving you well for years.

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