Navien Water Heater Not Producing Hot Water - Your Pro Troubleshooting

There are few things more jarring than stepping into the shower, expecting a wave of comforting heat, and getting a blast of icy-cold water instead. You know you have a high-efficiency, top-of-the-line Navien tankless water heater, so what gives? It’s a frustrating moment we see all the time here at HVACRLY.

I agree, it’s incredibly frustrating. But here’s my promise to you: we can figure this out together. The good news is that when a navien water heater not producing hot water is the problem, the unit’s own diagnostic system often points you directly to the solution. It’s usually a safety feature kicking in, not a catastrophic failure.

In this comprehensive guide, we’ll walk through the exact steps a technician would take to diagnose the issue. We will preview how to read error codes, perform simple DIY checks on filters and vents, and understand when it’s time to put the tools down and call a licensed professional. Let’s get that hot water flowing again.

Why Your Navien Tankless Heater Is So Smart (And Why It Sometimes Stops)

Before we dive into troubleshooting, it helps to understand what makes your Navien unit tick. Unlike a traditional tank that keeps dozens of gallons of water hot 24/7, your tankless heater is an on-demand system. It’s a marvel of efficiency.

When you turn on a hot water faucet, a flow sensor detects the moving water and signals the control board. The board then opens the gas valve, sparks the igniter, and fires up the burner. Water flows through the heat exchanger, absorbing heat instantly before traveling to your faucet. This process is one of the key benefits of navien water heater not producing hot water solutions—when it works, it saves a ton of energy.

However, this entire sequence is monitored by a network of sensors. If any sensor detects a problem—no flame, poor airflow, a blocked filter, or overheating—the system will immediately shut down for safety. That’s why your hot water suddenly stops. The unit is protecting itself and your home.

Your First Step: Decoding the Navien Error Code

Your Navien’s front control panel is your best friend in this situation. It’s the first place you should look. When the unit stops working, it will almost always display an error code. This code is the starting point for our entire diagnostic process.

Don’t worry about memorizing them all. Just find the two or three-digit code on the display. Here are a few of the most common codes related to a navien water heater not producing hot water:

E003 (or 003E): Ignition Failure. The unit tried to light the burner but failed to detect a flame. This could be a gas supply issue or a problem with the igniter itself.
E012 (or 012E): Flame Loss. The burner lit successfully but the flame went out unexpectedly. This often points to gas pressure problems or venting issues.
E710 (or 710E): Abnormal Flow Sensor. The unit is not detecting water flow correctly, so it doesn’t know it needs to turn on. This is very often caused by a clogged filter.
E110 (or 110E): Blocked Venting or High Wind. The pressure sensor has detected an issue with the air intake or exhaust, preventing safe operation.

Once you have your error code, you have a solid clue. Now, let’s move on to the hands-on checks you can safely perform.

Common Problems with Navien Water Heater Not Producing Hot Water: Your DIY Checklist

Armed with your error code (or even without one), you can work through a few safe, simple checks. This section is your essential navien water heater not producing hot water guide. Before you open the unit’s cover, always turn off the power to the water heater at the circuit breaker for safety.

Check 1: Power and Gas Supply (The Obvious Stuff)

It sounds too simple, but you’d be surprised how often this is the culprit. We get service calls for this all the time. Let’s make sure the basics are covered.

Check the Power: Is the unit plugged in securely? Go to your electrical panel and check if the breaker for the water heater has tripped. If it has, flip it back on once. If it trips again immediately, do not touch it again and call an electrician.
Confirm the Gas Supply: Find the gas line leading to your Navien unit. There should be a small valve with a handle. Ensure the handle is parallel (in line) with the pipe, which means it’s open. If it’s perpendicular, it’s closed. Also, check if other gas appliances in your home (like a stove) are working to confirm your gas service is active.

Check 2: The Water Flow Sensor and Inlet Filter

This is one of the most common problems we see, especially if you have hard water. The flow sensor can’t do its job if it’s blocked by sediment. This is a primary tip in our how to navien water heater not producing hot water troubleshooting process.

Inside the cold water inlet pipe on your Navien, there is a small screen filter. Over time, tiny bits of minerals and debris can clog it up, reducing water flow to the point where the sensor doesn’t activate the heater.

To check and clean the inlet filter safely:

Turn off the power at the breaker.
Shut off the gas using the valve on the gas line.
Close the main water valves to the unit. There will be a blue handle (cold) and a red handle (hot) on the isolation valves below the unit. Turn them perpendicular to the pipe to close them.
Place a small bucket under the cold water inlet to catch any drips.
Carefully unscrew the cold water line connection. Just behind it, you should see the small screen filter. You may need to gently pull it out with a pair of needle-nose pliers.
Rinse the filter thoroughly under a sink until it’s clean. If it’s heavily calcified, you can soak it in vinegar for 15 minutes.
Re-insert the filter, re-connect the water line, and slowly turn the water, gas, and power back on.

Check 3: Inspecting the Air Intake and Exhaust Vents

Your Navien heater needs to breathe. It pulls in fresh air for combustion and pushes out exhaust fumes. If either of these vents is blocked, the unit’s safety sensors will shut it down immediately, often triggering an E110 error code.

Go outside and find where your PVC vent pipes terminate. Look for any obstructions like leaves, snow, bird nests, or debris. Clear away anything that might be blocking the openings. This simple step is one of the most effective navien water heater not producing hot water tips for restoring operation.

Check 4: Addressing Low Water Pressure or Flow Rate

Tankless heaters require a minimum amount of water flow to activate—typically around 0.5 gallons per minute (GPM). If the flow rate is too low, the heater won’t turn on.

First, check the aerators on your faucets. Unscrew the tip of the faucet and check the small screen for debris. A clogged aerator can restrict flow enough to prevent the heater from firing. If the problem is only happening at one sink, this is almost certainly the cause.

Advanced Troubleshooting: When to Call a Professional

If you’ve run through the DIY checklist and still have no hot water, the problem likely lies with an internal component. For your safety, these issues should always be handled by a licensed and insured HVAC or plumbing professional.

Ignition and Flame Rod Issues

If you hear your Navien clicking repeatedly but it never fully fires up (an E003 code is common here), the problem is likely with the ignition system. The igniter might be cracked, or the flame sensor rod could be coated in carbon, preventing it from detecting the flame.

While cleaning a flame rod is technically simple, it involves working directly in the combustion chamber next to the gas components. Due to the inherent risks of dealing with gas and combustion, this is a job best left to a trained technician.

Internal Leaks or Component Failure

Persistent error codes that don’t clear, or any sign of water dripping from the bottom of the unit, point to a more serious internal problem. This could be a failing pump, a compromised heat exchanger, or a faulty control board. These are complex and expensive parts that require professional diagnosis and replacement.

The Importance of Regular Maintenance: Your Navien Water Heater Care Guide

The absolute best way to deal with a navien water heater not producing hot water is to prevent it from happening in the first place. An annual maintenance routine is crucial for the health and longevity of your tankless unit. Following these navien water heater not producing hot water best practices will keep it running efficiently for years.

A well-maintained unit is also a sustainable navien water heater not producing hot water solution. By keeping the heat exchanger clean, you ensure it uses the minimum amount of gas necessary, making it an eco-friendly navien water heater not producing hot water strategy.

Annual Descaling (Flushing): This is the single most important maintenance task. Over time, minerals (limescale) build up inside the heat exchanger, acting like insulation and forcing the unit to work harder. Eventually, the buildup can restrict water flow and cause a shutdown. Flushing the unit with a vinegar or descaling solution removes this buildup.
Inlet Filter Cleaning: As described above, clean this filter every 6-12 months.
Vent Inspection: Check the intake and exhaust vents for blockages seasonally.
Professional Tune-Up: Have a technician inspect the unit annually to check gas pressure, clean the flame sensor, and ensure all components are in safe working order.

Frequently Asked Questions About Navien Water Heater Not Producing Hot Water

How do I reset my Navien water heater?

The simplest way to perform a soft reset is to unplug the unit from the wall outlet (or turn off its breaker), wait about 60 seconds, and then restore power. This can sometimes clear a temporary fault, but if a persistent error code returns, it means there is an underlying issue that needs to be addressed.

Why is my Navien water heater making a clicking sound but not heating?

That clicking sound is typically the electronic igniter trying to spark and light the gas. If it clicks but you get no flame (and likely an E003 error), it means the ignition sequence is failing. After confirming your gas is on, this points to a faulty igniter, a dirty flame sensor, or a gas valve problem, all of which require a professional technician.

Can I descale my Navien water heater myself?

Yes, many homeowners successfully descale their own units. The process involves using a small submersible pump, a bucket, and a couple of hoses to circulate a descaling solution (like food-grade vinegar) through the unit for about 45-60 minutes. Navien provides instructions in their user manuals, and many video tutorials are available online. If you’re not comfortable with the process, a plumber can perform the service for you.

How often should I service my Navien tankless water heater?

We strongly recommend annual service. The most critical part of this service is descaling the heat exchanger, especially if you live in an area with hard water. A yearly check-up ensures your unit runs safely, efficiently, and reliably.

Troubleshooting a high-tech appliance like a Navien water heater can feel intimidating, but by following a logical process—checking codes, verifying the basics, and cleaning filters—you can often solve the problem yourself. Remember to always prioritize safety and never hesitate to call a qualified professional when you’re out of your comfort zone.

With these tips, you’re well-equipped to tackle the problem and understand what’s happening inside that smart little box. Stay safe, and enjoy that 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.