How Often Should You Flush A Navien Tankless Water Heater: A Pro'S

You invested in a Navien tankless water heater for its promise of endless, on-demand hot water and incredible energy efficiency. It’s a brilliant piece of technology. But have you noticed it’s taking just a little longer to heat up, or that the pressure at your showerhead isn’t quite what it used to be? It’s a common experience, and it’s often the first whisper that your unit needs a little TLC.

We’re here to promise you that one simple, regular maintenance task can restore that “like-new” performance, protect your investment, and prevent costly breakdowns. It’s not a secret reserved for the pros; it’s something you can absolutely handle.

In this complete guide, we’ll walk you through exactly how often should you flush a navien tankless water heater, why it’s so critical for its health, and provide a clear, step-by-step process to do it safely yourself. Let’s keep that hot water flowing perfectly.

Why Flushing Your Navien Isn’t Just a Suggestion—It’s Essential

Think of your Navien’s heat exchanger as the heart of the system. It’s a maze of intricate copper piping where water is rapidly heated as it flows through. The problem is, your water isn’t just pure H₂O; it contains dissolved minerals like calcium and magnesium.

When this water is heated, these minerals precipitate out and stick to the inside of the pipes, forming a hard, crusty layer called limescale. This buildup acts like an insulator, forcing your Navien to work much harder and burn more gas to heat the water to your desired temperature.

This process has several negative effects:

Reduced Efficiency: The scale barrier means less heat transfers to the water, causing your energy bills to creep up.
Flow Restriction: As the pipes narrow with scale, you’ll notice a drop in water pressure and flow throughout your home.
Component Strain: Overheating caused by scale can damage the heat exchanger—the most expensive part of your unit—leading to premature failure.
Error Codes: A heavily scaled unit can trigger flow-related error codes, causing frustrating shutdowns.

Understanding the benefits of how often should you flush a navien tankless water heater is simple: it directly combats all these issues, keeping your unit running efficiently and reliably for its entire lifespan.

The Official Recommendation: How Often Should You Flush a Navien Tankless Water Heater?

Alright, let’s get right to the core question. As a general rule of thumb, you should plan to flush your Navien tankless water heater at least once every 12 months. This is the baseline recommendation for most homes.

However, the single most important factor that dictates your flushing schedule is your local water hardness. This isn’t a one-size-fits-all situation; your water quality determines your maintenance needs.

Understanding Your Local Water Hardness

Water hardness is measured in “grains per gallon” (GPG) and refers to the concentration of dissolved calcium and magnesium. The higher the GPG, the “harder” the water, and the faster scale will build up inside your heater.

Not sure how hard your water is? It’s easy to find out. You can often find a water quality report on your municipal water supplier’s website. Alternatively, you can buy an inexpensive water hardness test kit online or from a local home improvement store.

Flushing Frequency Based on Water Hardness (GPG)

Once you know your GPG, you can use this simple how often should you flush a navien tankless water heater guide to create a precise schedule:

Soft Water (0-3 GPG): You have great water! You can likely extend your flushing interval to every 18-24 months.
Moderately Hard Water (4-7 GPG): This is average for many areas. Stick to the standard once every 12 months schedule.
Hard Water (8-10 GPG): You have a higher mineral content. You should flush your unit more frequently, about every 9-12 months.
Very Hard Water (10+ GPG): With this level of hardness, scale builds up rapidly. Plan to flush every 6-9 months. We also strongly recommend installing a whole-house water softener to protect not just your Navien, but all of your plumbing and appliances.

The Telltale Signs: When Your Navien Is Begging for a Flush

Sometimes your water heater will give you clear signals that it’s overdue for service. Don’t ignore these symptoms, as they are often precursors to bigger issues. These are the most common problems with how often should you flush a navien tankless water heater that signal it’s time for maintenance.

Look out for these signs:

Fluctuating Water Temperatures: Does your shower get hot, then lukewarm, then hot again? This inconsistency is often caused by a struggling, scaled-up unit.
Reduced Hot Water Pressure: If the flow from your hot water taps seems weaker than the cold, it’s a classic sign of mineral buildup constricting the pipes.
Longer Wait for Hot Water: If it feels like it’s taking noticeably longer for hot water to reach your faucets, the insulated heat exchanger is likely to blame.
Rumbling or “Kettling” Noises: A low rumbling or popping sound from the unit is a serious red flag. This is the sound of water getting trapped under layers of scale and boiling—a condition called kettling that puts immense stress on the heat exchanger.
Error Codes: Navien units are smart. An error code like E012 can indicate a flow issue, which is frequently caused by scale obstruction.

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

Ready to tackle this yourself? Great! It’s a very manageable DIY project. Don’t worry—we’ll walk through these how to how often should you flush a navien tankless water heater steps together. Set aside about 90 minutes to do it right.

Step 1: Gather Your Tools & Materials

Having everything ready beforehand makes the process smooth and stress-free. Here’s what you’ll need:

A 3 to 5-gallon bucket
A small submersible utility pump (a 1/6 HP pump is perfect)
A set of two laundry machine hoses (at least 3-4 feet long)
2-3 gallons of food-grade white vinegar or a commercial descaling solution approved for potable water systems
Channel-lock pliers or an adjustable wrench

Step 2: The Flushing Process (Step-by-Step)

Follow these steps carefully. Safety is always the top priority.

Power Down for Safety: Go to your electrical panel and turn off the breaker for your Navien unit. If it’s a plug-in model, simply unplug it. Next, locate the gas shut-off valve on the line leading to the heater and turn it to the “Off” position (the handle should be perpendicular to the pipe).
Isolate the Water Heater: Locate the three water valves connected to your unit. They are typically color-coded: a red handle for hot, a blue handle for cold, and a main valve on the cold inlet. Close all three by turning the handles perpendicular to the pipes. This stops water from entering or leaving the unit.
Connect Your Hoses: Your Navien has service ports on the hot and cold water lines. Carefully use your pliers to remove the caps from these ports. Attach one of your hoses to the cold water (blue) service port and the other hose to the hot water (red) service port.
Prepare the Descaling Solution: Pour your white vinegar or descaling solution into the 5-gallon bucket. There should be enough liquid to fully submerge your submersible pump.
Create the Cleaning Loop: Place the submersible pump at the bottom of the bucket. Connect the other end of the hose from the cold water (blue) port to the outlet on your pump. Place the open end of the hose from the hot water (red) port into the bucket, ensuring it will stay put. You’ve now created a closed loop for cleaning.
Open the Service Valves: Slowly turn the small handles on the service ports so they are parallel with the valves. This opens the ports and allows the cleaning solution to circulate through the heater. Your main valves should still be closed.
Circulate and Clean: Plug in your submersible pump. You should see the vinegar being pumped into the cold side, circulating through the heat exchanger, and flowing back out the hot side into the bucket. Let this run continuously for at least 45 to 60 minutes. For very hard water, you can let it run for up to 90 minutes.
Flush with Fresh Water: After circulating, unplug the pump. Close the hot (red) service valve. Remove the hose from the pump and point it into the bucket to drain. Now, keeping the main cold valve closed, open the main cold water inlet valve slightly. This will push clean water through the unit, flushing out the vinegar and any dislodged scale into the bucket. Let it flush for 5-10 minutes until the water runs clear.
Clean the Inlet Filter (Pro Tip!): Before putting everything back, unscrew the cold water inlet connection. Inside, you’ll find a small screen filter. Remove it, rinse it thoroughly to remove any sediment, and put it back. This is one of the most important how often should you flush a navien tankless water heater tips that many people miss!
Restore to Service: Close the main cold water inlet valve and the cold (blue) service valve. Disconnect both hoses and securely replace the service port caps. Now, slowly open all three main water valves (hot, cold, and main inlet).
Power Up and Test: Restore power to the unit by flipping the breaker back on or plugging it in. Turn the gas valve back to the “On” position. Go to the nearest hot water faucet and turn it on. It may sputter at first as air works its way out. Let it run until you have a steady stream of hot water. Congratulations, you’re done!

Best Practices for a Sustainable and Eco-Friendly Flush

Maintaining your Navien is not just good for your wallet; it can also be done in an environmentally conscious way. Following this eco-friendly how often should you flush a navien tankless water heater approach ensures you’re being responsible.

Choosing the Right Descaling Solution

While powerful commercial descalers exist, plain old white vinegar is often the perfect choice. It’s non-toxic, food-safe, biodegradable, and highly effective at dissolving calcium carbonate scale. It’s a simple, sustainable how often should you flush a navien tankless water heater practice that gets the job done without harsh chemicals.

Water Conservation and Solution Disposal

After the flush, the vinegar solution is acidic but easily neutralized. You can safely dispose of it by diluting it with plenty of water as you pour it down a drain. The small amount of water used during the flushing step is far less than the water wasted by an inefficient heater over the course of a year. By keeping your unit at peak efficiency, you are reducing its gas consumption and overall carbon footprint every single day.

Frequently Asked Questions About Navien Tankless Flushing

Can I use CLR or other harsh chemicals to flush my Navien?

Absolutely not. Navien and other manufacturers strongly advise against using harsh, aggressive chemicals like CLR. They can damage the sensitive copper components and rubber seals inside the unit, potentially voiding your warranty. Always stick to food-grade white vinegar or a solution specifically designed and approved for potable tankless water heaters.

What happens if I never flush my tankless water heater?

Ignoring this maintenance will lead to a cascade of problems. You’ll experience a gradual but certain decline in performance, higher energy bills, and reduced water flow. Eventually, the scale buildup can become so severe that it permanently damages the heat exchanger, leading to a repair that can cost almost as much as a new unit. It’s the number one cause of premature tankless water heater failure.

How much does it cost to have a professional flush my Navien?

If you’re not comfortable with the DIY approach, hiring a qualified plumber or HVAC technician is a great option. The cost for a professional flush typically ranges from $150 to $300, depending on your location and the service company. This fee often includes a basic inspection of the unit, making it a worthwhile investment for peace of mind.

My Navien is making a loud rumbling noise. Is that a sign it needs flushing?

Yes, that is a critical warning sign. That rumbling or “kettling” sound is the noise of water being superheated and boiling in pockets trapped beneath the limescale buildup. It puts extreme thermal stress on the heat exchanger. If you hear this, you should schedule a flush immediately to prevent permanent damage.

Following this how often should you flush a navien tankless water heater care guide is the single most effective action you can take to ensure you get the long life and high performance you expect from your investment. Taking an hour once a year will be rewarded with many years of reliable, wonderfully efficient hot water.

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.