Navien Tankless Water Heater Will Not Turn On - A Pro'S

You turn the shower handle, expecting a rush of comforting hot water, but all you get is a cold, disappointing stream. You wait. And wait. But the familiar, quiet roar of your Navien tankless heater never kicks in. It’s a frustrating moment that can throw your whole day off course.

We get it. That silence from the utility closet is stressful. But here’s the good news: many times when a Navien tankless water heater will not turn on, the cause is something simple you can safely identify and even fix yourself. You don’t always need to make that expensive service call right away.

We promise to walk you through the exact same diagnostic steps a professional technician would take, from the most basic checks to understanding what your heater is trying to tell you. This guide will empower you to troubleshoot with confidence, restore your hot water, and learn some essential maintenance tips along the way.

Let’s get that hot water flowing again. We’ll start with the easiest things first.

Before You Panic: The First 3 Simple Checks

Before we dive into error codes or internal parts, let’s cover the “oops” moments. Over 50% of service calls for a dead unit end with one of these three simple fixes. Checking them first can save you time, money, and a lot of headaches.

Check for Power: Is the Unit Plugged In and Getting Juice?

It sounds almost too simple, but you’d be surprised how often this is the culprit. Your Navien is a sophisticated appliance that needs a constant supply of electricity to operate its circuit board, display, and igniter.

Is it plugged in? Look for the power cord and ensure it’s firmly seated in the wall outlet.
Check the outlet. Many Navien units are plugged into a GFCI (Ground Fault Circuit Interrupter) outlet—the kind with “TEST” and “RESET” buttons. If the button has popped out, press RESET firmly until it clicks.
Inspect the circuit breaker. Head to your home’s main electrical panel. Look for the breaker labeled “Water Heater” or similar. If it’s in the middle or “OFF” position, flip it firmly to “OFF” and then back to “ON”.

Verify Gas Supply: Is the Gas Valve Open?

No fuel means no flame. Your water heater needs a steady supply of natural gas or propane to heat the water. Often, a gas valve gets turned off accidentally during other home maintenance.

Follow the gas line from your heater. You should find a small valve with a handle. The handle should be parallel (in line) with the pipe to be open. If the handle is perpendicular (making a “T” shape) to the pipe, it’s closed. Turn it slowly so it’s parallel to the pipe.

Confirm Water Flow: Is There Enough to Activate the Heater?

Your Navien has a built-in flow sensor. It’s a safety and efficiency feature that prevents the unit from firing up unless it detects a sufficient amount of water flowing through it (typically around 0.5 gallons per minute).

Check Faucet Aerators: Unscrew the tip of the faucet where the water comes out. If the small screen inside is clogged with sediment, it can reduce flow and prevent the heater from activating. Clean it and try again.
Open the Hot Water Tap Fully: Try turning on a large fixture, like a bathtub faucet, all the way to “hot.” If this triggers the heater but a single sink doesn’t, it points to a flow rate issue.
Check the Inlet Filter: We’ll cover this more in maintenance, but a clogged inlet water filter is a very common reason for low flow.

Understanding Your Navien’s Brain: Reading the Error Codes

If the basics check out, it’s time to let the unit tell you what’s wrong. One of the best features of a Navien is its diagnostic display. An error code is your most powerful clue in this troubleshooting guide.

How to Find and Interpret Your Error Code

On the front of your Navien unit, there is a small digital display. If the system has detected a fault, it will typically flash an error code, often starting with the letter “E” followed by three numbers (e.g., E001, E012).

If the screen is blank, you likely have a power issue (go back to the first step!). If it’s on but showing no code, the unit may not have registered a fault yet. Running a hot water tap for a minute can sometimes trigger the fault and display the code.

What Common Navien Error Codes Mean

While your user manual has a full list, here are a few of the most common codes you might see when your Navien tankless water heater will not turn on:

E001 or E010 (Ignition Failure): The unit tried to light the burner but failed. This could be a gas supply issue, a dirty igniter, or a blocked vent.
E003 (Flame Loss): The burner lit successfully but then the flame went out unexpectedly. This often points to venting issues, gas pressure problems, or a dirty flame sensor.
E012 (Low Water Flow): The unit is not detecting enough water movement to safely fire up. This confirms what we discussed in the “flow” check above—look for clogged filters and aerators.
E711 (Condensate Drain Blocked): High-efficiency units like Navien produce condensation. If the drain line is blocked or frozen, a safety switch will shut the unit down.

The “Reset” Button: When and How to Use It Safely

After you’ve identified and potentially fixed an issue (like opening a gas valve or clearing a vent), you may need to reset the unit. You can do this by simply unplugging the water heater for 30 seconds and plugging it back in. This power cycle forces the internal computer to restart its sequence. Don’t just keep resetting it without addressing the underlying code; that won’t solve the problem.

Common Problems with Navien Tankless Water Heater Will Not Turn On

If you’ve gone through the initial checks and reviewed the error codes, you can start narrowing down the physical culprits. These are some of the most frequent issues our technicians encounter in the field.

Ignition System Failure

The igniter and flame sensor are two small, critical components. The igniter creates the spark to light the gas, and the flame sensor confirms a flame is present. Over time, these can become coated with residue and fail to work properly. Cleaning them is a job best left to a professional, but recognizing the symptom (clicking with no ignition) is a key diagnostic step for you.

Blocked Intake or Exhaust Vents

Your Navien needs to breathe. It pulls in fresh air for combustion and pushes out exhaust fumes. These PVC pipes usually run to the outside of your house. Always check that these vent terminations are clear.

Look for bird nests, leaves, snow, or any other debris that could be blocking the openings. A blockage will starve the unit of air and trigger a shutdown as a safety measure.

Frozen Condensate Line

In colder climates, this is a top-tier problem. The condensate drain line, a small plastic tube, can freeze solid where it exits your home. The unit’s internal sensor will detect the backup and prevent the heater from running to avoid water damage. Carefully thawing this line with a hairdryer or warm water can often bring your heater back to life instantly.

Essential Maintenance: Your Navien Tankless Water Heater Will Not Turn On Care Guide

The best way to fix a problem is to prevent it. Following some navien tankless water heater will not turn on best practices for maintenance is key to a long, efficient life for your unit. This is the core of any good care guide.

Flushing and Descaling to Prevent Mineral Buildup

If you live in an area with hard water, mineral scale (calcium and magnesium) will build up inside the delicate pipes of your heat exchanger. This forces the unit to work harder and can eventually restrict water flow, causing it to shut down. Flushing the unit annually with a vinegar solution is the single most important piece of maintenance you can perform for a long and eco-friendly navien tankless water heater lifespan.

Cleaning the Inlet Water Filter

This is a five-minute job that solves a surprising number of “no hot water” calls. Where your cold water line enters the Navien, there is a small filter screen. Turn off the water, unscrew the filter housing, rinse the screen thoroughly, and reinstall it. This simple task is one of the most effective navien tankless water heater will not turn on tips.

When to Put Down the Tools and Call a Professional

DIY troubleshooting is empowering, but safety is paramount. There are clear signs that it’s time to stop and call a certified technician who is trained to work on Navien systems.

If You Smell Gas

This is not negotiable. If you smell gas near your water heater or anywhere in your home, do not touch any electronics, leave the house immediately, and call your gas company’s emergency line from a safe distance.

Internal Component Issues

If you suspect the problem is with the gas valve, circuit board, heat exchanger, or any other internal sealed component, it’s time for a pro. These repairs require specialized tools, training, and an understanding of gas and electronics that is not safe for a DIY approach.

Persistent Error Codes After a Reset

If you’ve addressed the likely cause of an error code (e.g., you’ve cleared the vents for an ignition failure code) but it keeps coming back after a reset, there’s a deeper issue that needs a professional diagnosis.

The Eco-Friendly Benefits of a Properly Maintained Navien

Keeping your Navien in top shape isn’t just about having reliable hot water. A well-maintained unit is a sustainable navien tankless water heater. When the heat exchanger is clean and the vents are clear, the unit operates at peak efficiency, using less natural gas to heat your water. This not only lowers your utility bills but also reduces your home’s carbon footprint, making a properly functioning unit an important part of an eco-friendly home.

Frequently Asked Questions About a Navien That Won’t Start

Why is my Navien clicking but not turning on?

That clicking sound is most likely the electronic igniter trying to create a spark to light the gas. If it clicks repeatedly without the “whoosh” of the burner lighting, it typically points to an ignition failure. This could be due to no gas supply, a blocked vent, or a dirty igniter/flame sensor assembly.

How do I reset my Navien tankless water heater?

The simplest and most effective way to reset the unit’s computer is to perform a power cycle. Unplug the unit from the wall outlet, wait for a full 30-60 seconds to allow the internal capacitors to discharge, and then plug it back in. This is often more effective than just using the power button on the front panel.

Can a dirty filter really stop my Navien from working?

Absolutely. The small, thimble-sized cold water inlet filter is a major culprit. If it gets clogged with sediment, it can restrict water flow to a point where the flow sensor doesn’t register enough movement to tell the unit it’s safe to turn on. It’s a tiny part that can cause a total shutdown.

Troubleshooting a silent water heater can feel daunting, but by following these steps, you are well-equipped to diagnose the most common issues safely. You’ve checked the power, gas, and water flow, learned to decipher error codes, and understand the importance of routine care.

Remember to always prioritize safety. If you ever feel unsure or the problem seems to be inside the unit’s sealed cabinet, don’t hesitate to call a qualified Navien technician. You’ve done the hard work of narrowing down the problem, which will make their job faster and your repair bill smaller.

You’ve got this! Stay safe, and enjoy that well-earned hot shower.

Author
Recent Posts

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.