Navien Water Heater Error 773 00: Your Guide To A Fast & Safe Fix

That cold shock in the middle of a shower is a universal feeling of dread. You go to check your tankless water heater, and there it is—a blinking, unfamiliar code. If you’re seeing the navien water heater error 773 00, your first thought might be frustration, but don’t worry. We’re here to walk you through it.

Here at HVACRLY, we believe in empowering homeowners. This error code might seem technical, but it often points to a simple problem you can safely investigate yourself. Think of me as your friendly technician, guiding you through the process one step at a time.

This comprehensive navien water heater error 773 00 guide will break down exactly what this code means, show you how to safely troubleshoot it, and help you understand when it’s time to call for backup. Let’s get that hot water flowing again.

First, What Does Navien Error 773 00 Actually Mean?

Before we start turning knobs or opening panels, let’s understand the message your Navien unit is sending. In the world of tankless water heaters, error codes are like a secret language, and Code 773 00 is all about water flow.

Simply put, the navien water heater error 773 00 indicates a “No Water Flow Detected” issue. Your water heater is smart; it won’t try to heat water that isn’t moving through the unit. This is a crucial safety feature to prevent the heat exchanger from overheating and sustaining serious damage.

The unit’s internal flow sensor is waiting to detect a specific rate of water movement before it fires up the burner. When it doesn’t sense that movement—or senses it’s too low—it shuts down the heating process and displays this error code to protect itself.

Common Causes: Uncovering the Root of the Problem

Understanding why the water isn’t flowing is the key to solving the puzzle. Several common problems can trigger this error, and most are relatively straightforward. Think of it as being a detective for your plumbing system.

Here are the most frequent culprits behind a 773 00 error:

Low Water Pressure: The municipal supply to your home might be low, or a pressure-reducing valve could be failing.
Closed or Partially Closed Valves: It sounds simple, but service valves on the water lines leading to and from the unit might have been accidentally turned.
Clogged Inlet Water Filter: This is a big one. A small screen filter on the cold water inlet is designed to catch sediment and debris, and it can easily get clogged over time.
A Failed Flow Sensor: The sensor itself could be stuck, dirty, or have failed electronically, tricking the unit into thinking there’s no flow even when there is.
Internal Blockage or Airlock: Less common, but air trapped in the lines or a blockage within the unit’s plumbing can also impede flow.

Now that we know what we’re looking for, let’s get hands-on with some safe troubleshooting. We’ll start with the easiest fixes first.

Your Step-by-Step Guide to Troubleshooting Navien Water Heater Error 773 00

Alright, let’s roll up our sleeves. For these steps, you won’t need any special tools besides maybe a bucket and a pair of pliers. Remember, safety is always the priority. If you ever feel unsure or uncomfortable, stop and call a professional. Here is how to navien water heater error 773 00 troubleshooting should be approached.

Step 1: The Simple Reset (Power Cycle)

Before you do anything else, let’s try a simple reset. Sometimes, control boards can experience a temporary glitch. A quick power cycle can clear the error and get things working again.

Unplug the Navien unit from the wall outlet or turn off the circuit breaker that powers it.
Wait for at least five full minutes. This allows the internal capacitors to fully discharge and the system to reset completely.
Plug the unit back in or flip the breaker on.
Try running a hot water tap and see if the error code returns. If it does, move on to the next step.

Step 2: Check Your Valves and Water Pressure

Next, let’s make sure water can actually get to the heater. This seems basic, but it’s one of the most common problems with Navien water heater error 773 00.

Look at the pipes connected to the bottom of your unit. You should see three pipes, each with a valve handle. Make sure the handles on the hot (red) and cold (blue) water lines are parallel to the pipe, which indicates they are fully open. The handle on the main gas line (yellow) should also be parallel to its pipe.

While you’re at it, check other faucets in your house. Is the cold water pressure lower than usual everywhere? If so, the issue might be with your home’s main water supply, not the heater itself.

Step 3: Inspect and Clean the Water Inlet Filter

This is the most common fix, so pay close attention! The cold water inlet has a small screen filter to protect the unit’s sensitive components from sediment. When this clogs, it chokes off the water supply and triggers the error.

Turn off the power to the unit again. Safety first!
Close the water valves. Turn the handles on the hot (red) and cold (blue) service valves so they are perpendicular to the pipes. This isolates the unit.
Relieve the pressure. Open the small pressure relief valves (they look like little levers on the main service valves) to drain the remaining water. Have a small bucket ready to catch it.
Locate the filter. On the cold water inlet (the blue valve), you’ll see a large brass plug. Using pliers or a wrench, carefully unscrew this plug.
Remove and clean the filter. Inside, you’ll find a small, thimble-shaped screen. Gently pull it out. You’ll likely see it’s full of sand, scale, or other gunk. Rinse it thoroughly under a faucet until it’s perfectly clean. You can use an old toothbrush to gently scrub it.
Reassemble. Place the clean filter back in, screw the plug back on (hand-tight plus a quarter-turn with a wrench is enough), close the pressure relief valves, and slowly re-open the main water valves.
Restore power and test. Turn the power back on and try running hot water. For many homeowners, this is the magic fix!

Step 4: Examine the Flow Sensor (Advanced)

If the filter was clean and the error persists, the issue might be the flow sensor itself. It’s a small part with a paddle wheel or magnetic sensor inside that measures water movement. Debris can sometimes jam it.

You can sometimes dislodge minor debris by opening and closing a hot water tap several times in quick succession, creating small bursts of pressure. If this doesn’t work, inspecting or replacing the flow sensor is a job best left to a qualified technician, as it involves opening the unit’s casing and handling more delicate components.

Safety First: When to Stop and Call a Licensed Technician

Your safety is more important than a hot shower. While the steps above are generally safe for a capable DIYer, there are clear signs that you’ve reached the limit of what you should attempt on your own.

Call a licensed and insured HVAC or plumbing professional immediately if:

You are not comfortable performing any of the steps listed above.
You suspect a water leak inside the unit’s casing.
After cleaning the filter and resetting the unit, the error code persists.
The issue seems to be with the flow sensor or other internal components.
You smell gas or see any signs of burning or electrical malfunction.

A professional has the diagnostic tools, training, and replacement parts to accurately identify and fix complex issues with the flow sensor, circuit board, or internal plumbing. Trying to fix these yourself can lead to further damage or create an unsafe situation.

Preventative Maintenance: Best Practices to Avoid Future Errors

Fixing the problem is great, but preventing it is even better. Adopting a few navien water heater error 773 00 best practices can save you from future cold showers and extend the life of your unit. Think of this as your long-term navien water heater error 773 00 care guide.

Clean the Inlet Filter Regularly: Make cleaning that little screen filter part of your semi-annual home maintenance routine. If you have hard water or well water, you may need to do it quarterly.
Annual Professional Service: Have a qualified technician perform an annual service. They will descale the heat exchanger to remove mineral buildup, check all sensors, and ensure the unit is running at peak efficiency. This is a key part of having a sustainable and eco-friendly navien water heater.
Install a Water Softener: If you live in an area with hard water, a whole-home water softener is the single best investment you can make. It dramatically reduces the scale and sediment that clogs filters and damages internal components.

The Hidden Benefits of Resolving Error 773 00 Correctly

It might just seem like you’re fixing an annoying problem, but properly addressing this error code has wider benefits. The benefits of navien water heater error 773 00 resolution go beyond just getting hot water back.

When you clear a flow restriction, you restore your unit’s efficiency. A clogged filter makes the pump work harder and can reduce performance, leading to higher energy consumption. By ensuring clear water flow, you’re ensuring your heater operates as designed, saving you money on utility bills and promoting a more sustainable navien water heater operation.

Frequently Asked Questions About Navien Error 773 00

Can I fix error 773 00 myself?

In many cases, yes. The most common cause is a clogged inlet water filter, which is a straightforward cleaning task for a confident DIYer. Following the steps in this guide for resetting the unit, checking valves, and cleaning the filter can often resolve the issue without a service call.

How much does it cost to fix a Navien error 773 00?

If you can fix it yourself by cleaning the filter, the cost is $0. If you need to call a professional, the cost will vary based on your location and the root cause. A simple service call to clean the filter might be $100-$250. If the flow sensor needs to be replaced, the cost could be in the $250-$500 range, including parts and labor.

Does this error mean my water heater is broken?

Not necessarily. In fact, this error code is often a sign that the water heater’s safety systems are working perfectly! It’s protecting the most expensive component—the heat exchanger—from damage due to a lack of water flow. More often than not, it’s an issue with the water supply to the unit, not the unit itself.

How can I prevent this error from happening again?

The best prevention is regular maintenance. Clean the inlet water filter every 6-12 months, and schedule an annual professional descaling service, especially if you have hard water. A whole-home water softener is also highly effective at preventing the sediment and scale buildup that causes this error.

Tackling a water heater error can feel intimidating, but you’ve taken the first step by seeking out information. By following this guide, you can safely diagnose the most common causes of the navien water heater error 773 00 and, in many cases, fix it yourself.

Remember to trust your instincts. If a step feels too complex or you’re not seeing results, don’t hesitate to call a trusted local pro. Here’s to fast fixes and long, hot showers! 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.