Navien Tankless Water Heater E736 Error Code – A Pro’S Fix-It Guide

ByDavid Clark

There’s nothing quite like the jolt of an unexpectedly cold shower to disrupt your morning routine. You head to your Navien tankless water heater, and there it is—a cryptic message flashing on the display: E736. It’s frustrating, confusing, and immediately makes you worry about a costly repair.

Don’t worry. As technicians, we see these codes all the time. Think of it as your water heater’s way of telling you exactly what’s wrong so you can fix it. We promise to help you understand what this error means and walk you through safe, simple steps to diagnose and potentially resolve the issue yourself.

In this complete navien tankless water heater e736 error code guide, we’ll break down what’s happening inside your unit, explore the most common culprits, provide a step-by-step troubleshooting process, and clarify exactly when it’s time to call for professional backup. Let’s get your hot water flowing again.

What Exactly Is the Navien E736 Error Code?

First things first, let’s demystify the code. The official Navien definition for error code E736 is “DHW Outlet Temperature Sensor Open Circuit.”

In plain English, this means your water heater’s main control board has lost communication with the sensor that measures the temperature of the hot water leaving the unit. This sensor is a critical safety component.

Think of it like a chef trying to cook a delicate sauce without a thermometer. Without knowing the exact temperature, the chef can’t guarantee a perfect result and might even burn the dish. Similarly, your Navien shuts down because it can’t verify the water temperature, protecting you from potentially scalding hot water or other system malfunctions. It’s a built-in safety feature, not just a random glitch.

Common Causes Behind the E736 Fault

While a control board issue sounds serious, the E736 error is most often caused by something much simpler. Before you assume the worst, let’s look at the usual suspects. Understanding these common problems with navien tankless water heater e736 error code is the first step to a solution.

  • Loose or Disconnected Wiring: This is, by far, the most frequent cause. The vibrations from normal operation can sometimes cause the wire harness connecting the sensor to the control board to wiggle loose.
  • Damaged or Frayed Wires: Over time, a wire could get pinched, chewed by a pest, or simply wear out, creating a break in the connection. This “open circuit” is exactly what the error code describes.
  • Corrosion on the Connections: In areas with high humidity or if a tiny leak has occurred nearby, the metal pins on the sensor’s connector can corrode. This corrosion acts as a barrier, blocking the electrical signal.
  • A Failed Temperature Sensor: The sensor itself can eventually fail. Like any electronic component, it has a lifespan. When it dies, it can no longer send a signal to the control board, triggering the E736 code.
  • A Faulty Control Board (PCB): This is the least likely scenario, but it is possible. If the port on the Printed Circuit Board (PCB) where the sensor plugs in has failed, the board itself will need to be replaced. This is strictly a job for a qualified technician.

Your Step-by-Step Guide: How to Navien Tankless Water Heater E736 Error Code

Alright, let’s roll up our sleeves. For the DIY-capable homeowner, a simple visual inspection can often solve this problem. We’ll walk through a few safe checks together. Your safety is the number one priority, so if you feel unsure at any point, stop and call a professional.

Here is our recommended process following navien tankless water heater e736 error code best practices.

  1. Step 1: Safety First! Power Down Everything.

    Before you even think about removing the cover, you must cut all power to the unit. This isn’t just a suggestion—it’s a critical safety command.

    First, unplug the unit from the wall outlet or shut off the corresponding circuit breaker in your electrical panel. Then, locate the gas shut-off valve on the line leading to your water heater and turn it to the “Off” position. Your safety is non-negotiable.

  2. Step 2: Remove the Front Cover.

    Most Navien units have a few screws along the bottom or sides of the front panel. Remove these screws and gently lift the cover off. Set it aside somewhere safe. Refer to your owner’s manual if you’re unsure how to do this for your specific model.

  3. Step 3: Locate the DHW Outlet Temperature Sensor.

    Now you’re looking at the internal components. Don’t be intimidated. The DHW (Domestic Hot Water) outlet sensor is typically located on the main hot water pipe exiting the heat exchanger. It looks like a small probe or clip attached to the pipe with a wire harness leading from it.

    Your unit’s technical manual will have a diagram showing its exact location. It’s often labeled “Outlet thermistor” or something similar.

  4. Step 4: Inspect the Wiring and Connections.

    This is the moment of truth. Carefully trace the wire from the sensor back to where it plugs into the main control board (the PCB). Here’s what to look for:

    • Is the plug firmly seated in its socket on the board? Gently push on it to ensure it’s snug.
    • Are there any signs of corrosion (a white or greenish powder) on the connector pins?
    • Do the wires appear frayed, pinched, or broken anywhere along their length?

    One of our top navien tankless water heater e736 error code tips is to take a quick photo with your phone before you touch anything. This gives you a reference point. If the connection is loose, unplug it, look for any visible issues on the pins, and plug it back in securely until you hear or feel a click.

  5. Step 5: Reset and Test the System.

    If you found and secured a loose connection, you may have just fixed the problem. With the cover still off (for now), it’s time to test.

    Turn the gas valve back on, then restore power by plugging the unit in or flipping the breaker. The unit will go through its startup cycle. If the E736 error code is gone, congratulations! You’ve likely solved it. Turn on a hot water tap to confirm it’s working properly before putting the cover back on.

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When It’s Time to Call a Licensed Technician

The DIY checks above are designed to solve the most common and simple cause of the E736 error. However, there are clear signs that you’ve reached the limit of a safe DIY repair.

Please call a qualified HVAC or plumbing professional immediately if:

  • You are not 100% comfortable performing any of the steps above.
  • The error code persists after you’ve checked and secured the wiring.
  • You see any signs of water leakage, burn marks, or significant corrosion inside the unit.
  • You suspect the sensor or the control board is faulty. These parts require testing with a multimeter and specialized knowledge to replace correctly.

A professional technician has the tools to test the sensor’s resistance (ohms) to confirm if it has failed. They can safely replace the sensor or, in the rare case it’s needed, the main control board, ensuring your system runs safely and efficiently. The benefits of navien tankless water heater e736 error code professional service include peace of mind, safety, and protecting your warranty.

Preventing Future Errors: A Proactive Care Guide

An error code often serves as a wake-up call for maintenance. Adopting a proactive navien tankless water heater e736 error code care guide can prevent this and other issues from happening in the future, extending the life of your investment.

The Importance of Annual Descaling

The single most important maintenance task for any tankless water heater is annual flushing, also known as descaling. Minerals like calcium and magnesium in your water build up inside the heat exchanger and on components like sensors. This scale buildup can insulate the sensor, causing faulty readings, or even lead to its premature failure.

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Performing an annual flush is an eco-friendly navien tankless water heater e736 error code prevention strategy. A clean unit operates at peak efficiency, using less energy to heat your water. This is a sustainable practice that saves you money and reduces your carbon footprint.

Regular Visual Inspections

Once a month, take a quick look at and around your unit. Check for any signs of dripping water, ensure the air intake and exhaust vents are clear of obstructions, and listen for any unusual noises during operation. Catching small problems early prevents them from turning into error codes later.

Frequently Asked Questions About the Navien Tankless Water Heater E736 Error Code

Can I just reset my Navien unit to clear the E736 error?

You can certainly try resetting the unit by unplugging it for a few minutes and plugging it back in. However, if the error was triggered by a physical issue like a loose wire or a failed sensor, the code will almost certainly reappear as soon as the unit tries to operate. A reset doesn’t fix the underlying problem.

How much does it cost to fix a Navien E736 error?

The cost can vary widely. If a technician finds a simple loose wire, you may only pay for a service call fee. If the DHW outlet temperature sensor needs to be replaced, you can expect to pay for the part plus about an hour of labor. A control board replacement is the most expensive repair, but it’s also the least common cause of this specific error.

Is the E736 error code dangerous?

The error code itself is not dangerous; it is a safety alert. It prevents your water heater from operating in a potentially unsafe state where it cannot control the water temperature. The real danger lies in attempting complex electrical or gas-related repairs without proper training and tools. Always prioritize safety.

Facing a navien tankless water heater e736 error code can be daunting, but armed with the right knowledge, you can approach it with confidence. By following these safe, logical steps, you can identify the simple fixes and know exactly when it’s time to lean on the expertise of a professional.

Remember that consistent maintenance is the key to a long and efficient life for your tankless water heater. A little proactive care goes a long way in ensuring you always have the hot water you depend on.

Stay safe and stay comfortable!

David Clark
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