Fix Navien Tankless Heater Swings: Maintenance & Troubleshooting

Experiencing temperature swings with your Navien tankless water heater can be more than just a nuisance; it’s a disruption to your daily comfort. You’re not alone if you’ve noticed the water temperature fluctuating during a shower or when running the tap. This article dives into the common causes of these temperature swings and offers practical solutions to stabilize your hot water supply.

We’ll explore everything from maintenance tips to system settings that could be affecting your heater’s performance. Stay tuned as we unravel the mystery behind those unexpected cold bursts and scalding surprises, ensuring you’re well-equipped to tackle the issue head-on.

Common Causes of Temperature Swings

When experiencing temperature fluctuations with your Navien tankless water heater, it’s essential to identify the root causes. Here’s a breakdown of common problems you may encounter:

  • Faulty Flow Sensors: Flow sensors play a vital role in detecting water movement and signalling the heater to adjust temperature. If they malfunction, the water temperature can vary unexpectedly.
  • Clogged Filters: Reduced water flow due to clogged filters can cause brief cold water inserts during a hot shower as the system struggles to maintain a consistent output.
  • Gas Supply Issues: Inconsistent gas pressure or supply can lead to variations in water heating, resulting in temperature swings.
  • Venting Problems: Proper venting is critical for safe operation and performance of your tankless water heater. Obstructed or improper venting can negatively impact heat exchange and temperature stability.
  • Mixing Valves Malfunction: If the thermostatic mixing valve, which blends hot and cold water to your desired temperature, is not working correctly, it might fail to regulate the water temperature accurately.
  • System Overload: When multiple taps or appliances are used simultaneously, the demand may exceed the system’s capacity, causing a drop in temperature.

To mitigate these issues:

  • Regularly inspect and clean the filters.
  • Ensure a stable gas supply with periodic service checks.
  • Verify that the venting system adheres to the manufacturer’s guidelines.
  • Consider upgrading the mixing valve if it’s outdated or malfunctioning.
  • Schedule routine maintenance to prevent system overload and check for early signs of component wear and tear.

Understanding these causes helps pave the way for targeted solutions, ensuring your tankless water heater delivers reliable hot water without the hassle of sudden temperature shifts.

Maintenance Tips for Your Navien Tankless Water Heater

Regular upkeep of your Navien tankless water heater is essential for long-lasting performance and consistent temperature control. Proper maintenance not only extends the life of your appliance but also prevents unexpected temperature swings.

First and foremost, schedule annual servicing with a certified technician. These professionals are trained to identify and address any underlying issues that may not be immediately apparent to you. During a service visit, they’ll inspect the combustion chamber, check the condition of ignition rods, and look for any signs of wear or damage.

Regularly clean your air and water filters to avoid dirt and debris from placing undue strain on the system. Blocked filters can decrease efficiency and lead to temperature fluctuations. Here’s what you need to do:

  • Shut off the power to the heater.
  • Locate the filters. Your model’s user manual should provide specific instructions on where to find them.
  • Gently remove and clean the filters under running water.
  • Reinsert them after ensuring they are completely dry.

The heat exchanger should also be descaled at least once a year, especially if you live in an area with hard water. Scaling can reduce the heat transfer efficiency and result in fluctuating water temperatures. You can descale the exchanger by circulating a specially formulated descaling solution through the system.

Monitoring for error codes is another proactive measure you can take. Navien heaters come equipped with self-diagnostic systems that can alert you to issues needing immediate attention. Addressing these error codes swiftly can prevent minor issues from escalating.

Lastly, ensure that your gas supply is stable and meets the unit’s demands. Fluctuations in gas pressure can cause erratic heating performance. A qualified technician can verify gas line size and pressure to ensure they align with your specific Navien model’s requirements.

By following these straightforward maintenance tips, you’ll help secure a continuous supply of hot water and minimize the chances of experiencing disruptive temperature variations in your Navien tankless water heater.

Understanding System Settings and Their Impact

When dealing with temperature swings in your Navien tankless water heater, understanding the system settings is crucial. This understanding allows you to optimize performance and avoid unexpected fluctuations in water temperature.

The Modulating Temperature Control is a key feature of your Navien unit. This technology adjusts the burner’s heat output in real-time, based on the water flow rate and desired temperature. If not set correctly, it might lead to inconsistent water temperatures.

Additionally, the Water Flow Rate setting plays a significant role. Navien heaters require a minimum flow rate to trigger heating. Too low of a setting can lead to cold spells, while too high may cause unnecessary strain on the system.

  • Adjust the Minimum Flow Rate if you’re experiencing delayed hot water.
  • Monitor the Maximum Flow Rate to prevent the system from overworking.

The Temperature settings on your unit also directly impact the hot water output. Navien units often come with a default temperature which may not align with your personal needs.

  • You can increase energy efficiency by setting the heater to your ideal temperature instead of a higher default setting.
  • Consider seasonal adjustments to account for incoming water temperature variations.

Make sure the system’s firmware is up to date. Outdated firmware can lead to miscommunication within the system, which can result in temperature instability.

Regularly checking and adjusting these settings not only provides immediate comfort but also ensures the longevity and efficiency of your tankless water heater.

Troubleshooting Temperature Fluctuations

When you’re experiencing temperature swings with your Navien tankless water heater, it’s crucial to troubleshoot effectively. Strategically diagnose the issue to ensure a swift resolution.

Check the Water Flow Rate
If the flow rate is below the minimum required, your water heater may struggle to maintain a consistent temperature. Ensure that your faucets and showers are outputting enough water by:

  • Cleaning aerators and filters to remove blockages
  • Checking for closed valves or kinks in the piping that may restrict flow

Examine Water Usage
Simultaneous water usage across different outlets can lead to fluctuations. Make sure you’re not running multiple appliances at the same time that require hot water.

Inspect the Incoming Water Temperature
Seasonal changes can affect the temperature of the incoming water. A larger variance in the outside temperature may mean your heater has to work harder to adjust.

Evaluate System Installation
An improperly installed system could cause inconsistent water temperatures. Double-check that your:

  • Gas lines are sized correctly
  • Venting system is installed as per manufacturer guidelines

Assess the Mixing Valve
Faulty mixing valves can lead to irregular water temperatures. If the valve is not blending hot and cold water correctly, consider replacing or repairing it.

Remember, it’s important to maintain consistency in your maintenance routine. Regularly check your system’s set-up and don’t hesitate to call a professional if you’re unable to pinpoint the problem yourself. Performing these steps helps to minimize the risk of temperature fluctuations and ensures a steady supply of hot water.

Practical Solutions to Stabilize Your Hot Water Supply

If you’re experiencing temperature swings with your Navien tankless water heater, there are practical steps you can take to stabilize your hot water supply.

Check the Flow Sensor
The flow sensor is critical in dictating the water heater’s operation. If it’s not functioning properly, it could be the culprit for inconsistent temperatures. Make sure it’s clean and unobstructed.

  • Adjust the Temperature Settings
    If your water heater fluctuates, consider setting a stable temperature on the control panel. Consistent settings can minimize the chances of sudden temperature changes.

Inspect for Cross-Connection
Cross-connection in your plumbing system can cause cold water to mix with hot, resulting in temperature instability. A professional inspection can identify and rectify this issue.

Upgrade Showerheads and Faucets
Low-flow fixtures may not provide enough water to keep the heater activated. Upgrading to compatible showerheads and faucets can ensure a steady flow that maintains consistent temperature.

Consider a System Redesign
If your system’s design is flawed, even minor adjustments won’t suffice. Consulting with a certified technician on a system redesign can resolve chronic instability issues.

By tackling these aspects, your hot water supply should become more stable, providing the comfort and reliability you need for your daily hot water usage.


You’re now equipped with the know-how to tackle those pesky temperature swings in your Navien tankless water heater. Remember, regular maintenance and being proactive with troubleshooting can go a long way in ensuring a consistent hot water supply. Don’t hesitate to reach out to a professional if you’re ever in doubt. With your new-found knowledge and a bit of diligence, you’ll enjoy the comfort of steady, reliable hot water day in and day out.