How To Descale A Navien Tankless Water Heater - A Pro'S Step-By-Step

Is your morning shower turning lukewarm faster than it should? Are you noticing a drop in hot water pressure or hearing strange gurgling sounds from your Navien tankless water heater? It’s a common headache for homeowners, but the culprit is often a simple, fixable problem: mineral scale buildup.

Don’t worry—this isn’t a sign that your high-efficiency unit is failing. It’s a routine maintenance task you can absolutely handle yourself. We’re here to walk you through exactly how to descale a navien tankless water heater safely and effectively, just like a seasoned technician would.

This comprehensive guide will give you the confidence to restore your unit’s performance, boost its efficiency, and extend its lifespan. Picture steady, piping-hot water on demand and lower energy bills. Let’s get that hot water flowing strong again!

Why Descaling Your Navien is Non-Negotiable

Before we roll up our sleeves, let’s talk about why this is so important. Over time, minerals naturally present in your water supply—primarily calcium and magnesium—cling to the inside of your water heater’s delicate heat exchanger. This chalky buildup is called “scale.”

Think of it like plaque in an artery. This layer of scale acts as an insulator, forcing your Navien to work much harder to heat the water. This leads directly to a few big problems:

Reduced Efficiency: Your unit burns more gas to achieve the same temperature, driving up your utility bills.
Lower Water Flow: The scale can physically constrict the water passages, leading to frustratingly low hot water pressure.
Component Strain: Overheating caused by scale buildup can damage critical components, leading to expensive repairs and even premature failure of the unit.
Error Codes: Severe scaling can trigger fault codes on your Navien’s display, like E012 (flame loss) or E003 (abnormal exhaust), as the unit struggles to operate correctly.

The benefits of how to descale a navien tankless water heater are clear. A simple annual flush keeps it running like new, protecting your investment and ensuring you have reliable hot water when you need it most.

Gathering Your Tools & Materials: The Descaling Kit

Having everything ready beforehand makes the process smooth and stress-free. You can buy pre-made descaling kits, but it’s just as easy to assemble your own. Here’s your checklist:

A 5-Gallon Bucket: This will hold your cleaning solution.
A Submersible Pump: A small utility pump rated for at least 350 gallons per hour (GPH) is perfect.
Two 3/4″ Hoses: A pair of standard washing machine hoses works beautifully. Make sure they have rubber gaskets inside the fittings.
Descaling Solution: You have a couple of great options here. For a sustainable and eco-friendly how to descale a navien tankless water heater solution, use 2 gallons of plain white vinegar. For tougher scale, a commercial descaler like Flow-Aide is highly effective.
Channel-Lock Pliers or an Adjustable Wrench: For loosening and tightening hose connections.
Old Towels & Gloves: To manage any drips and protect your hands.

With your tools laid out, you’re ready to begin. This entire process should take you about 90 minutes, with most of that time being hands-off while the pump does the work.

Your Step-by-Step Guide: How to Descale a Navien Tankless Water Heater

Alright, let’s get to it. Follow this how to descale a navien tankless water heater guide carefully, and your unit will be clean in no time. We’ve broken it down into simple, manageable steps.

Step 1: Safety First! Isolate the Unit

Your safety is the absolute top priority. Before you touch anything, you must shut off all power and fuel sources to the water heater.

Turn Off Electricity: Unplug the Navien unit from the wall outlet or switch off the corresponding breaker in your electrical panel.
Turn Off Gas: Locate the gas shut-off valve on the line leading to your water heater. The handle should be perpendicular (forming a “T”) to the pipe to be in the “off” position.
Shut Off Water: Close the main hot and cold water valves that feed your Navien. These are typically color-coded—blue for cold, red for hot.

Step 2: Connect Your Hoses to the Service Ports

Your Navien is equipped with service ports specifically for this process. They have circular handles and are located on the main hot and cold water valves.

Unscrew the caps from the service ports. A little water may drip out, which is normal.
Connect one hose to the cold water (blue) service port.
Connect the second hose to the hot water (red) service port.

Hand-tighten the hoses, then give them a gentle quarter-turn with your pliers to ensure a snug, leak-free seal.

Step 3: Prepare the Descaling Solution

Place your 5-gallon bucket directly below the unit. If you’re using vinegar, pour two gallons of white vinegar into the bucket. If using a commercial descaler, follow the manufacturer’s instructions for dilution—most require mixing with water.

Step 4: Create the Cleaning Loop

This is where the magic happens. You’re going to create a closed loop to circulate the cleaning solution through the heat exchanger.

Place your submersible pump at the bottom of the bucket, fully submerged in the solution.
Take the hose connected to the cold water (blue) service port and attach its other end to the outlet of your submersible pump.
Place the loose end of the hose connected to the hot water (red) service port into the bucket. Make sure it stays in the bucket to avoid spills.

Step 5: Circulate the Solution

It’s time to start the cleaning process. Open the two service port valves by turning their small handles so they are parallel with the pipes. Now, plug in your submersible pump.

You should see the solution being pumped from the bucket, into the cold side of your Navien, through the heat exchanger, and back out the hot side into the bucket. Let this run uninterrupted for at least 45 to 60 minutes. You might see the solution get cloudy or change color as it dissolves the mineral scale—that’s a good sign it’s working!

Step 6: Flush the System Thoroughly

Once the circulation is complete, you need to flush all the descaling solution out of the unit with fresh water. This is a critical step, so don’t skip it!

Unplug the submersible pump.
Close the hot water (red) service port.
Keep the cold water (blue) service port open.
Remove the hose from the hot water port and point it into the bucket or a nearby drain.
Slowly open the main cold water inlet valve that you closed in Step 1. This will push fresh water through the unit, flushing out the vinegar and debris.
Let the water flush through for a good 5-10 minutes until it runs completely clear and you no longer smell vinegar.

Step 7: Reconnect and Restart

You’re in the home stretch! It’s time to put everything back to normal.

Close the main cold water inlet valve and the cold water service port.
Disconnect both of your hoses and screw the service port caps back on securely.
Slowly open the main hot and cold water valves to the unit.
Restore power by plugging the unit back in or flipping the breaker on.
Restore the gas supply by turning the valve handle parallel to the pipe.

Step 8: Check Your Work

Go to the nearest faucet and turn on the hot water. It may sputter at first as air works its way out of the lines. Let it run for a few minutes. Check the Navien unit and your hose connections for any signs of leaks. If all is dry and you have strong hot water flow, congratulations—you’ve successfully completed the job!

Pro Tips and Best Practices for Navien Descaling

Learning how to descale a navien tankless water heater is one thing, but mastering it is another. Here are some pro tips from the field to ensure you get the best results every time.

How Often Should You Descale?

This depends entirely on your water hardness. In areas with very hard water, you should descale annually. For homes with moderate to soft water, every 18-24 months is usually sufficient. When in doubt, once a year is a great rule of thumb and is one of the most important how to descale a navien tankless water heater best practices.

Don’t Forget the Inlet Filter!

While the unit is depressurized, it’s the perfect time to clean the small screen filter on the cold water inlet. It’s usually located right where your main cold water line connects to the unit. Simply unscrew it, pull out the screen, rinse it clean of any sediment, and pop it back in. This prevents debris from entering the unit in the first place.

Vinegar vs. Commercial Descaler

Vinegar is an excellent, non-toxic, and affordable option for routine maintenance. However, if it’s been several years since the last flush or you have extremely hard water, a commercial descaler formulated for potable water systems will work faster and more aggressively on heavy buildup.

Common Problems and When to Call a Professional

Even with a perfect guide, you might run into a snag. Here are a few common problems with how to descale a navien tankless water heater and how to handle them.

Problem: Leaks at the Service Valves

If you see a drip from your hose connections, turn everything off and check the rubber gaskets inside the hose fittings. If one is missing or cracked, it won’t seal properly. This is a common issue with older hoses.

Problem: Still Low Pressure After Descaling

If you’ve descaled the unit and cleaned the inlet filter but still have low pressure, the issue might be elsewhere. It could be a clogged fixture aerator or a more serious blockage inside the unit’s flow sensor. If the problem persists, it’s time to call a certified Navien technician.

The “When to Bail” Rule

This DIY project is very manageable, but know your limits. If you feel unsure at any step, see signs of a significant leak, or the unit continues to display error codes after you’re done, stop what you’re doing. Turn off the water, gas, and power, and call a professional. Your safety and your equipment are worth more than a service call fee.

Frequently Asked Questions About Descaling a Navien Heater

Can I use CLR to descale my Navien?

No, we strongly advise against it. While CLR is a powerful descaler, it contains harsh chemicals that can damage the sensitive rubber seals, gaskets, and even the metal components inside your Navien’s heat exchanger. Stick to food-grade white vinegar or a descaler specifically approved for potable water systems.

What does the Navien descaling error code look like?

Navien units don’t have a specific “time to descale” code. Instead, scale buildup causes performance issues that trigger other codes. The most common are E012 (flame loss) or E003 (abnormal exhaust), which can happen when the heat exchanger is so coated in scale that it can’t transfer heat to the water properly, causing the unit to overheat and shut down.

How long does it take to descale a Navien tankless water heater?

Plan for about 90 minutes to two hours from start to finish. The actual hands-on time for setup and flushing is only about 30 minutes. The other 45-60 minutes are for the pump to circulate the solution, which is a great time to grab a coffee.

Is it worth installing a water softener to prevent scale?

Absolutely. If you live in an area with hard water, a whole-home water softener is the single best investment you can make. It’s the ultimate how to descale a navien tankless water heater care guide tip because it stops scale before it ever starts, protecting not just your water heater but all your pipes and water-using appliances.

By taking an hour or two each year to perform this simple maintenance, you are ensuring your Navien tankless water heater operates at peak efficiency, saving you money and providing endless, reliable hot water for years to come.

You’ve now got the knowledge and the steps to keep your Navien in top shape. Regular maintenance is the key to comfort and peace of mind. Stay safe, and enjoy the hot water you’ve earned!

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.