Navien Water Heater Keeps Running - Your Expert Guide To Why And How

You hear it, don’t you? That persistent, low hum from your Navien tankless water heater, long after you’ve turned off the shower or kitchen sink. It’s a sound that can make you wonder if everything is okay, and you’re right to question it. That constant operation isn’t just a minor annoyance; it’s a signal that your high-efficiency unit might be wasting energy and water, or that a component needs attention.

You’ve come to the right place for answers. As HVACR professionals, we’ve diagnosed this exact issue countless times. The good news is that often, the root cause is something you can identify and even fix yourself safely. We promise to guide you through the process, step by step, just like we would on a service call.

In this comprehensive guide, we’ll explore why your Navien water heater keeps running, from the most common culprit—tiny, hidden leaks—to internal components like flow sensors. We’ll also help you understand your unit’s normal recirculation functions so you can tell the difference between a problem and peak performance. Let’s get that heater running only when you need it to.

Understanding Why Your Navien “Runs” Differently

First, let’s set the stage. Unlike a traditional tank-style heater that periodically fires up to keep 40 or 50 gallons of water hot, your Navien is a tankless, or “on-demand,” unit. It’s designed to heat water only when you need it. This is the core of its energy efficiency.

When you turn on a hot water tap, a device called a flow sensor detects the movement of water. This sensor is the “on” switch; it tells the unit’s powerful burner to ignite and the heat exchanger to get to work. When you turn the tap off, the sensor signals the unit to shut down.

So, if the unit is running when no taps are open, it means the flow sensor thinks water is moving. Our job is to figure out why.

The #1 Culprit: The Hidden Hot Water Drip

In our experience, more than 80% of the time a Navien water heater keeps running, the cause is an undetected hot water leak somewhere in your home. Navien’s flow sensors are incredibly sensitive—they need to be to provide instant hot water. They can detect a flow rate as low as 0.1 to 0.2 gallons per minute (GPM).

This means a leak you might not even notice is enough to trick your heater into firing up. Here’s where to look for these sneaky water thieves.

Common Leak Locations to Check

Faucets: Check every single faucet in your home (kitchen, bathrooms, utility sink). A slow drip, especially from the hot side, is a prime suspect.
Showerheads and Bathtub Taps: A leaky showerhead or tub spout is another common source. Sometimes the leak is so slight it evaporates before you see it, so listen closely.
Toilets: This is a big one people miss. If the flapper in your toilet tank isn’t sealing properly, it can slowly leak water into the bowl. If your toilet’s fill valve is connected to the hot water line (uncommon, but possible) or if you have a mixing valve for a bidet, this could be the cause.
Washing Machine & Dishwasher: Check the hot water connection hoses behind these appliances for any signs of moisture.
Outdoor Spigots: If you have an outdoor hose bib or sink connected to a hot water line, ensure it’s turned off completely.

A Pro Tip for Finding Micro-Leaks

Here’s a simple trick we use in the field. Go to your water meter (usually located near the curb or in your basement). Most meters have a small, spinning triangle or dial on them called a leak indicator. Make sure no water is being used in the house, then watch that indicator for a few minutes. If it’s spinning, even very slowly, you have a leak somewhere.

Common Problems with Navien Water Heater Keeps Running: Internal Issues

If you’ve thoroughly checked for leaks and found nothing, the issue might be inside the water heater itself. This part of our navien water heater keeps running guide requires a bit more caution. Always turn off the power to your water heater at the circuit breaker before opening the front panel.

The Flow Sensor

The flow sensor is the brain’s first line of information. It’s a small part with a paddle wheel or magnetic sensor that measures water movement.

Debris or Scale Buildup: If you have hard water, mineral scale (limescale) can build up on the sensor, causing it to stick in the “on” position. This is a common problem if the unit hasn’t been descaled regularly as part of its care guide.
Sensor Failure: Like any electronic component, the flow sensor can fail over time. It might send a false positive signal to the main control board, telling it to fire up even with no water flow.

The Main Control Board (PCB)

The Printed Circuit Board (PCB) is the unit’s central computer. While less common, a faulty relay or a glitch on the board can cause the unit to run continuously. This is a more complex diagnosis and almost always requires a certified technician to test and replace the board.

Incorrect DIP Switch Settings

Navien units have a series of small “DIP switches” on the control board that configure its behavior, such as setting it up for an external recirculation pump. If these switches are set incorrectly for your home’s plumbing setup, it can cause erratic behavior. Unless you are 100% certain of what you are doing by following the installation manual, it’s best to leave these settings to a pro.

A Step-by-Step DIY Diagnosis Guide

Ready to play detective? Follow these steps in order. This is how to navien water heater keeps running troubleshooting should be approached: from easiest to most complex.

Observe the Unit’s Display: Your Navien’s front panel provides valuable clues. When the unit is running, look for a flame icon and a GPM (gallons per minute) reading. If it shows a small flow rate, like 0.2 GPM, it confirms the unit thinks water is flowing—pointing you back to a probable leak.
Perform a Full Leak Inspection: Use the checklist from the section above. Be meticulous. Spend a few minutes at each sink and shower, listening and looking for any sign of a drip. Don’t forget to check under sinks for moisture.
Isolate the Heater: A great way to confirm if the problem is in your house plumbing or the heater itself is to shut off the main hot water outlet valve on the heater. If the heater stops running after a minute, you have 100% confirmation the problem is a leak somewhere in your home’s hot water pipes or fixtures. If it continues to run, the issue is likely internal to the heater.
Check Recirculation Settings: If your model has an internal circulation pump and “Intelligent Pre-heating” (like the NPE-A series), check its settings. The unit might be in a learning mode or set to a schedule that you’re not aware of. Consult your manual to understand these modes.
Power Cycle the Unit: The classic “turn it off and on again” can sometimes resolve a temporary electronic glitch. Turn off the power at the breaker, wait a full five minutes, and then turn it back on.

If you’ve completed these steps and the heater is still running, it’s time to put down the tools. The problem is likely a faulty internal component that requires professional diagnosis.

Is It Running or Just Recirculating?

One of the best benefits of Navien water heater keeps running technology (when working correctly) is its recirculation capability. This feature eliminates the cold water sandwich and gives you hot water faster.

However, it can be confusing. The unit will run briefly to keep the water in the recirculation loop warm. This is normal and intentional.

NPE-A Series (Advanced): These models have a built-in pump and buffer tank. The “Intelligent Pre-heating” feature learns your hot water usage patterns and circulates water in anticipation. You might hear it run for short periods even when no taps are open. This is smart, eco-friendly navien water heater keeps running behavior designed to save water.
NPE-S Series (Standard): These units can be used with an external recirculation pump. The pump is what circulates the water, and the heater will fire to keep that loop hot based on the pump’s timer or aquastat.

The key difference is duration. Normal recirculation involves short, intermittent run cycles. A problem is indicated by continuous, non-stop operation for many minutes or hours.

Navien Water Heater Keeps Running Best Practices for Prevention

An ounce of prevention is worth a pound of cure, especially with high-tech appliances. Following a simple navien water heater keeps running care guide can save you headaches and money.

Annual Descaling: This is the single most important maintenance task. Flushing the unit with a vinegar or approved descaling solution removes the mineral buildup that can damage components like the heat exchanger and flow sensor. This is key to a sustainable and long-lasting unit.
Fix Leaks Immediately: Don’t ignore a dripping faucet. That tiny drip not only wastes hundreds of gallons of water per year but also causes unnecessary wear and tear on your tankless heater.
Check the Inlet Water Filter: Navien units have a small screen filter on the cold water inlet. Check and clean it every 6-12 months to prevent debris from entering the unit and damaging the flow sensor.

Frequently Asked Questions About a Navien Water Heater That Keeps Running

Why does my Navien make a clicking sound when it’s running?

The clicking sound is typically the spark igniter trying to light the burner or the sound of a solenoid valve opening and closing. This is normal during startup and shutdown sequences. However, if it clicks continuously without firing, it could signal an ignition problem, and you should call a technician.

Can I adjust the flow sensor sensitivity?

No, the flow sensor’s sensitivity is factory-calibrated and cannot be adjusted by the homeowner. Its high sensitivity is necessary for the “on-demand” feature to work correctly. The solution is to fix the source of the flow (the leak), not to change the sensor’s setting.

How much does it cost to fix a Navien that keeps running?

The cost varies wildly depending on the cause. If it’s a simple dripping faucet washer, the fix might cost a few dollars. If the internal flow sensor or main circuit board needs to be replaced by a professional, you could be looking at a repair bill of several hundred dollars, depending on parts and labor rates in your area.

Troubleshooting why your Navien water heater keeps running can feel daunting, but it’s often a straightforward process of elimination. By starting with the simplest and most common cause—a hidden leak—you can often solve the problem yourself and gain a better understanding of your home’s plumbing system.

Remember to prioritize safety. If you’re ever unsure or uncomfortable with a step, especially one that involves opening the unit’s panel, your best move is to call a qualified Navien technician. They have the tools and training to diagnose the issue quickly and safely.

Stay proactive with maintenance, fix those drips, and your Navien will provide you with efficient, on-demand hot water for years to come. Stay safe and stay comfortable!

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David Clark

Founder & Lead HVAC Specialist at HVACRLY

David Clark is the founder of HVACrly and a certified HVAC specialist with 10+ years working on residential and light-commercial systems. He turns complex heating, cooling, ventilation, and refrigeration topics into clear, actionable guides focused on safety and energy efficiency. When he’s not on a service call, he’s testing tools and writing step-by-step tutorials.