Tankless water heaters are fantastic machines, offering an endless supply of hot water and serious energy savings. Navien stands out as a leading brand in this space, known for high-quality engineering and durable stainless steel heat exchangers. If you install or service plumbing systems, you already know that Navien units are built to last. But even the best equipment needs a little TLC to keep running smoothly.
Understanding how to flush Navien tankless water heater units is a fundamental skill for any plumbing professional. Over time, the hard work of heating water leaves behind stubborn mineral deposits. If these deposits are ignored, they can wreak havoc on the system’s efficiency, reduce water flow, and ultimately shorten the lifespan of the unit.
In this comprehensive guide, we will walk through the exact steps for flushing a Navien tankless water heater. We will cover the tools you need, the signs that it is time for a flush, and how to troubleshoot common issues along the way. Whether you are prepping for a seasonal maintenance call or dealing with a sudden error code, this guide will help you get the job done efficiently and reliably.
Why You Need to Flush Your Navien Tankless Water Heater
Water is full of dissolved minerals, primarily calcium and magnesium. When water is heated rapidly inside a tankless unit, these minerals separate and cling to the internal walls of the heat exchanger. This chalky white buildup is commonly known as limescale or scale.
If you do not flush a tankless water heater regularly, that scale acts as an insulator. The heat exchanger has to work much harder to transfer heat through the thick layer of minerals and into the water. This causes a massive drop in energy efficiency. Your clients will likely notice their utility bills creeping up, even if their hot water usage has not changed.
Worse yet, heavy scale buildup can cause severe damage. The heat exchanger can overheat, leading to premature failure and potentially expensive repairs. Navien units are smart enough to detect these issues, often throwing an E016 error code (overheating) or an E003 error code (ignition failure due to restricted flow). Furthermore, failing to perform regular maintenance like flushing can void the manufacturer’s limited warranty. By flushing the unit, you remove this buildup, restore the heater’s efficiency, ensure consistent hot water delivery, and extend the overall lifespan of the system.
When to Flush Your Navien Tankless Water Heater
Navien recommends flushing their tankless water heaters at least once a year. However, this is just a baseline. The actual frequency depends heavily on the local water quality and the household’s hot water usage.
If you work in areas with notoriously hard water, such as Arizona, Nevada, or Texas, you might need to schedule maintenance every six to eight months. You can often tell it is time for a flush before the year is up by paying attention to a few key warning signs:
- Reduced water flow: Scale buildup physically clogs the narrow waterways inside the heat exchanger, resulting in weaker water pressure at the hot water taps.
- Fluctuating temperatures: If the water goes from hot to cold and back again, the heat exchanger is struggling to transfer heat consistently.
- Strange noises: Bubbling, knocking, or hissing sounds coming from the unit usually mean water is boiling erratically around thick scale deposits.
- Error codes: As mentioned, Navien error codes like E016 and E003 are strong indicators that the system is choked by scale and needs immediate attention.
Tools and Materials Required for Flushing
Before you head to the job site, make sure your truck is stocked with the right supplies. Having the correct equipment makes this process incredibly efficient. You can source all of these reliable plumbing supplies through PlumbersOnly.com, our efficient online ordering platform.
- Submersible pump: A small utility pump (around 1/6 horsepower) is perfect for circulating the cleaning solution.
- Two washing machine hoses: Standard hoses will connect the pump and the unit’s service ports.
- 5-gallon bucket: This will hold the descaling solution and the pump.
- Descaling solution: You can use 3 to 4 gallons of food-grade white vinegar (5% acetic acid). For a faster and more aggressive clean, use a commercial descaler approved for tankless heaters, such as Hercules Haymaker or Rectorseal Calci-Free.
- Phillips head screwdriver: Useful for accessing certain filter panels.
- Towels or rags: To catch any minor drips or spills.
- Safety goggles and gloves: Always protect your eyes and skin, especially when handling chemical descalers.
Step-by-Step Guide: How to Flush Your Navien Tankless Water Heater
With your tools ready, it is time to get to work. Follow these steps carefully to ensure a safe and effective flush.
Preparation
Safety and setup come first. Start by disconnecting the power to the Navien unit. You can simply unplug it from the wall outlet or flip the dedicated breaker. Next, shut off the gas supply valve leading to the unit.
Locate the main cold water supply valve and the main hot water outlet valve on the bottom of the heater. Turn both of these valves to the closed position. This isolates the water heater from the rest of the home’s plumbing system.
Now, locate the service valves (often called purge ports). There is one on the cold water side and one on the hot water side. These are usually capped off and have small handles. Keep them closed for now, but remove the caps. Be prepared with a towel, as a small amount of water may drip out.
Connecting the Hoses
Take your submersible pump and place it directly into the center of your 5-gallon bucket.
Attach one end of the first washing machine hose to the cold water service valve on the Navien unit. Attach the other end of this same hose to the discharge port on your submersible pump.
Take the second washing machine hose and attach one end to the hot water service valve on the unit. Place the open end of this hose directly into the 5-gallon bucket. This creates a closed loop: the pump pushes the solution into the cold side, it travels through the heat exchanger, and it flows out of the hot side back into the bucket.
Flushing Solution
Fill the 5-gallon bucket with your chosen descaling solution. If you are using white vinegar, pour in enough to fully submerge the pump (usually about 3 to 4 gallons). If you are using a commercial descaler like Calci-Free, mix it with water exactly according to the manufacturer’s instructions on the bottle. Ensure the pump intake is completely underwater so it does not draw in air.
Initiating the Flush
Turn the handles on both the cold and hot service valves to the open position.
Plug in your submersible pump to turn it on. You should immediately see the solution flowing out of the hot water hose and back into the bucket.
Let the pump run and circulate the solution continuously. If you are using white vinegar, you should let it circulate for a full 45 to 60 minutes to effectively dissolve the tough minerals. If you are using a commercial descaler, 20 to 30 minutes is typically sufficient. Keep an eye on the bucket; you might notice the liquid changing color or becoming cloudy as the scale breaks down and flushes out.
Draining and Rinsing
Once the circulation time is up, unplug the submersible pump to stop the flow.
Close the cold water service valve on the Navien unit. Leave the hot water service valve open, with its hose still draining into the bucket.
Now, open the main cold water supply valve on the unit. Fresh water will rush into the heater, flush out the remaining descaling solution, and pour out of the hot water service hose into your bucket. Let this run for about 5 to 10 minutes. If your bucket fills up, simply shut off the main cold water valve, empty the bucket, and resume the rinse. You want the water running completely clear and free of any vinegar or chemical smell.
After rinsing, close the hot water service valve. Disconnect both washing machine hoses from the service ports and securely replace the caps on the ports.
Restoring Operation
Open the main hot water outlet valve on the unit.
Go inside the house and open a few hot water faucets (like a bathroom sink or a bathtub). Let the water run for a few minutes. This purges any trapped air from the plumbing lines. Once the water flows smoothly without sputtering, turn the faucets off.
Turn the gas supply valve back on. Finally, plug the Navien unit back into the power outlet. The system will go through its startup sequence. Turn on a hot water tap and verify that the unit fires up correctly and delivers consistent hot water. Check all your valve connections underneath the unit to ensure there are no leaks.
Important Tips and Safety Precautions
Flushing a tankless unit is straightforward, but it requires attention to detail. Always read the specific owner’s manual for the exact Navien model you are working on, as slightly different configurations exist between the NPE-A, NPE-S, and NPE-2 series.
Never mix different types of descaling chemicals. Mixing chemicals can create toxic fumes or damage the internal components of the heater. If you are using a commercial product, ensure the area is well-ventilated.
Remind your clients that keeping a documented log of this annual maintenance is crucial. If a warranty claim ever needs to be filed, Navien will want to see proof that the unit was regularly flushed by a qualified professional.
Troubleshooting Common Flushing Issues
Sometimes things do not go exactly according to plan. Here are a few quick troubleshooting tips for common flushing hiccups.
Pump not circulating: If you plug in the pump and no liquid moves, check for airlocks. Ensure the pump is fully submerged. You may need to briefly loosen the hose connection at the cold service valve to bleed out trapped air, then tighten it back up.
Leaks after reconnecting: If the service ports drip after you replace the caps, check the rubber washers inside the caps. These can wear out over time. It is a good practice to keep spare washers in your toolkit.
Still experiencing E003 or E016 codes: If you flush the unit and it still throws an error code, the scale buildup might be excessively severe, requiring a secondary flush with a stronger commercial descaler. Alternatively, the issue might lie in a fouled flame rod or a clogged intake filter, requiring further inspection.
Maintaining Your Navien for Optimal Performance
Flushing the heat exchanger is the main event, but a complete maintenance check includes a few other vital components. Taking five extra minutes to clean these parts ensures a truly reliable system.
Clean the water inlet filter: Every Navien unit has a small screen filter on the cold water inlet to catch debris. Turn off the water, unscrew the filter, rinse it under cold water, and scrub it gently with a small brush. If you are working on an NPE-Advanced model, do not forget to clean the additional screen on the recirculation inlet.
Clean the intake air filter: Tankless heaters need a massive amount of air for combustion. Just inside the top of the cabinet, below the air intake collar, is an air screen. Pull this out, remove any dust, bugs, or lint with a toothbrush, and rinse it. Make sure it is completely dry before reinstalling it.
Clean the condensate trap: The trap at the bottom of the unit collects acidic condensation. Remove the metal wire clip, pull the cup out, empty it, and rinse it clean. When replacing it, ensure the O-ring is seated perfectly to prevent leaks.
For clients in extreme hard water areas, you might recommend installing a Navien PeakFlow anti-scale system on the cold water line. This chemical-free water treatment system changes the structure of the minerals before they enter the heater, preventing scaling before it starts and reducing the frequency of necessary flushes.
Keep Your Operations Flowing
Mastering how to flush Navien tankless water heater systems is just one way you provide incredible value to your clients. Preventative maintenance keeps their homes comfortable, lowers their bills, and builds immense trust in your services.
To keep your own operations running just as smoothly, you need a local supply partner you can trust. Van Marcke Plumbing Supply is here to support your business with competitive pricing, an extensive product range, and an incredible loyalty rewards program. You can easily stock up on submersible pumps, commercial descalers, washing machine hoses, and everything else you need for seasonal maintenance.
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