Navien Water Heater Error 736: Your Step-By-Step Fix And Prevention

There’s nothing quite like the jolt of an unexpectedly cold shower. You check your Navien tankless water heater, and instead of reassuring green or blue lights, you see a blinking screen with a cryptic message: Navien water heater error 736. It’s a frustrating moment that can throw your whole day off track.

But don’t worry—you’ve come to the right place. That error code isn’t just a random number; it’s a specific message from your unit’s brain, and we’re here to help you translate it. Think of us as your friendly technician, ready to walk you through the problem safely.

We promise this guide will demystify error 736, giving you the confidence to perform safe initial checks and understand exactly when it’s time to call in a professional.

In this complete navien water heater error 736 guide, we’ll break down what the code means, uncover its most common causes, and provide a clear, step-by-step troubleshooting plan. You’ll learn not just how to fix the problem now, but how to prevent it from ever coming back.

What Exactly Is Navien Error Code 736?

First things first, let’s get to the bottom of the code itself. Error 736 on a Navien unit indicates a “False Flame Detection”.

In simple terms, your water heater’s main control board (the PCB) believes it’s sensing a flame in the burner chamber when there shouldn’t be one. This typically happens when the unit is in standby mode or right after a heating cycle has finished.

This might sound strange, but it’s actually a critical safety feature. Your water heater is programmed to know that if no hot water is being called for, the gas valve should be closed and there should be absolutely no flame. When it detects one anyway, it immediately shuts down and displays error 736 to prevent a potentially dangerous situation, like gas flowing when it shouldn’t be.

Understanding this is the first step in our troubleshooting journey. The unit isn’t necessarily broken; it’s protecting itself—and you.

Uncovering the Common Problems with Navien Water Heater Error 736

So, why would your water heater think there’s a fire when there isn’t one? This “ghost flame” is almost always caused by an issue with the components designed to detect and manage the flame. Here are the most common culprits, from the simplest to the most complex.

A Dirty or Faulty Flame Sensor Rod

This is, by far, the most frequent cause of error 736. The flame sensor is a thin metal rod positioned in the path of the flame. Its job is to confirm that the gas has ignited successfully. It does this through a process called “flame rectification.”

Over time, this tiny rod can get coated with carbon buildup, soot, or mineral deposits. This dirty layer can act as a conductor, essentially tricking the control board into thinking a flame is present even after the gas valve has closed. It’s like having a smudge on your glasses—what you’re seeing isn’t quite real.

Moisture or Condensate Issues

Navien units are high-efficiency condensing heaters. This means they extract so much heat from the exhaust gas that water (condensate) forms. This water is supposed to drain away harmlessly through a condensate trap and drain line.

If that drain line becomes clogged with debris, the water can back up into the unit. This moisture can get on electrical components, including the flame sensor or its wiring, causing a short circuit that mimics the signal of a real flame.

A Malfunctioning Main Control Board (PCB)

The control board is the central nervous system of your water heater. While less common, the board itself can fail. A power surge, age, or an internal fault can cause the board to misread the signals it receives from the sensors.

If the board’s flame-sensing circuit is damaged, it might generate a false flame signal internally, triggering the error code even if all other components are working perfectly.

Poor Grounding or Electrical Interference

Your Navien water heater relies on a stable electrical ground to operate correctly. If the unit has a poor ground connection, or if there is other “electrical noise” from nearby appliances, it can interfere with the very weak electrical signal the flame sensor sends. This interference can be misinterpreted by the control board as a flame.

How to Navien Water Heater Error 736: A Safe Troubleshooting Guide

Alright, let’s roll up our sleeves. We’re going to walk through a few safe checks together. This process is designed to rule out the simple issues first.

IMPORTANT SAFETY WARNING: Before you open the cover of your water heater, you must turn off the power to the unit at your circuit breaker and shut off the gas supply using the manual shut-off valve on the gas line. Your safety is always the number one priority.

Perform a Simple Power Cycle (The “Reboot”)
Sometimes, a temporary glitch in the control board’s software can cause an error. The first and easiest step is to perform a full reset.
- Turn off the power to the water heater at the breaker box.
- Unplug the unit from the wall outlet if possible.
- Wait for at least 5-10 minutes. This allows any residual power in the control board’s capacitors to dissipate completely.
- Plug the unit back in and turn the circuit breaker back on.
If the error code disappears and doesn’t return, you may have just had a one-time glitch. However, if it comes back, it’s time to move to the next step.
Inspect the Condensate Drain Line
This is a common and easily fixable issue. Locate the clear or white plastic tube coming from the bottom of your Navien unit. This is the condensate drain.
- Check if the tube is kinked, pinched, or clogged with debris.
- Follow the tube to where it terminates. Is it blocked?
- Many Navien units have a small, clear condensate trap at the bottom. Check if it’s full of water and gunk. If so, it needs to be carefully removed and cleaned out with warm water. Be prepared with a small bucket to catch any water.
A clear drain path is one of the best navien water heater error 736 tips for maintaining a healthy unit.
Check for Obvious Loose Connections
With the power and gas still off, you can remove the front cover of the unit (usually held by a few screws at the bottom). Look inside without touching anything at first.
Visually inspect the wire leading to the flame sensor (it’s a single wire connected to a metal rod near the burners). Does the connection look secure? Look for any signs of corrosion (green or white buildup) or singed wires around the control board. If you see anything that looks burnt or damaged, stop immediately and call a professional.

When It’s Time to Call a Licensed Technician

Knowing your limits is the most important part of any DIY project. While the steps above are safe for most homeowners, error 736 can sometimes point to deeper issues that require professional tools and expertise.

You should call a qualified Navien technician if:

The error code returns immediately after a power cycle.
You are not 100% comfortable opening the unit’s cover or checking its components.
You suspect a problem with the control board or see signs of electrical damage.
You’ve checked the condensate drain and it’s clear, but the error persists.
The issue requires cleaning the flame sensor. While some experienced DIYers attempt this, it’s a delicate component that can be easily damaged. A pro can do it quickly and safely.

A professional has the right tools, like a multimeter, to properly test the flame sensor’s signal and diagnose a faulty control board, saving you time and preventing further damage.

Navien Water Heater Error 736 Best Practices for Prevention

The best way to deal with error 736 is to never see it in the first place. Following a simple navien water heater error 736 care guide can dramatically improve your unit’s reliability and efficiency.

Schedule Annual Professional Maintenance

This is the single most effective thing you can do. During an annual service, a technician will perform a deep clean, including:

Cleaning the flame sensor and igniter assembly.
Flushing the heat exchanger to remove scale buildup.
Cleaning the condensate trap and drain system.
Checking gas pressure and combustion settings.
Inspecting all safety controls.

Embrace a Sustainable, Eco-Friendly Approach

A well-maintained water heater is an energy-efficient one. When components like the flame sensor and heat exchanger are clean, the unit operates at peak performance. This means it uses less natural gas and electricity to heat your water.

Adopting a regular maintenance schedule is the most sustainable navien water heater error 736 solution. It extends the life of your appliance, reduces energy consumption, and lowers your carbon footprint—a win for your wallet and the planet.

Keep the Surrounding Area Clean

Your tankless water heater needs to breathe. Ensure the area around the unit is free from dust, lint, and debris. Never store flammable liquids, paint cans, or cleaning supplies nearby. A clean environment prevents contaminants from being pulled into the burner chamber, which helps keep internal components clean.

Frequently Asked Questions About Navien Water Heater Error 736

Is Navien error 736 a dangerous code?

The code itself is a safety notification, meaning the unit has shut down to prevent a dangerous condition. However, the underlying cause could be serious if ignored. It’s crucial to address the root problem rather than just resetting the unit repeatedly.

Can I just keep resetting my Navien heater if I get error 736?

No. A single reset might solve a temporary glitch, but if the error returns, it’s a clear sign of an underlying mechanical or electrical problem. Continually resetting the unit without fixing the issue can put stress on the components and potentially lead to a more costly repair down the road.

How much does it cost to fix a Navien error 736?

The cost can vary widely. If it’s a simple fix like clearing a clogged condensate drain, you might only pay for a standard service call fee ($150 – $300). If the flame sensor needs professional cleaning or replacement, it will be in that same range. However, if the main control board (PCB) has failed, the repair could cost between $600 and $1,200 or more, depending on the model and labor rates.

Tackling an error code on your Navien water heater can feel intimidating, but you’re now equipped with the expert knowledge to understand the problem and take the right steps. By following the safe checks and knowing when to call for backup, you can ensure your system runs safely and reliably.

Remember, preventative maintenance is your best defense against unexpected cold showers. A little care goes a long way in keeping the hot water flowing for years to come. Stay safe and stay comfortable!

Author
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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.