Winterizing Navien Tankless Water Heater – The Complete Pro Guide

As an HVACR technician, I’ve seen the aftermath of a winter freeze on an unprotected water heater. The sinking feeling when a homeowner realizes a tiny oversight has led to a cracked heat exchanger, a flooded utility room, and a very expensive emergency call is something we all want to avoid. You might even see a dreaded error code flash on your Navien’s display just when you need hot water the most.

It’s a common fear, but I’m here to promise you that it’s entirely preventable. Protecting your high-efficiency Navien unit isn’t complicated, and with the right guidance, it’s a task you can confidently handle yourself.

This comprehensive guide will walk you through the entire process of winterizing navien tankless water heater units. We’ll cover why it’s so critical, the exact tools you’ll need, the step-by-step draining procedure for long-term shutdowns, and how to safely rely on the unit’s built-in protection for shorter trips. Think of me as your personal tech, guiding you through each step to ensure your home stays warm and your water stays hot, all winter long.

Why Bother? The Critical Benefits of Winterizing Your Navien Tankless Water Heater

It’s easy to put off a maintenance task, but this is one you can’t afford to skip, especially if your unit is in an unheated space like a cabin, garage, or vacation home that will be vacant during cold snaps. The benefits of winterizing navien tankless water heater units go far beyond just checking a box on your to-do list.

Here’s what you gain with a few minutes of prevention:

Prevents Catastrophic Freeze Damage: Water expands when it freezes. Inside the delicate copper waterways of your Navien’s heat exchanger, that expansion can cause cracks and ruptures, leading to irreparable damage. A proper drain-down is the only guaranteed way to prevent this.
Ensures Hot Water Reliability: There is nothing worse than waking up to an ice-cold shower on a frigid morning. Winterizing ensures your unit is ready to perform flawlessly the moment you need it.
Extends the Lifespan of Your Investment: A Navien tankless water heater is a significant investment in your home’s comfort and efficiency. Protecting it from the single most common cause of premature failure—freeze damage—is the smartest way to maximize its service life.
Avoids Costly Emergency Repairs: An emergency call for a burst water heater is one of the most expensive and stressful situations a homeowner can face. The cost of a professional winterization service, or the half-hour it takes to do it yourself, is a tiny fraction of a replacement.
Gives You Total Peace of Mind: Knowing your home is protected while you’re away or during a severe storm allows you to relax. This winterizing navien tankless water heater care guide is your roadmap to that peace of mind.

Gathering Your Tools and Supplies: What You’ll Need

Before you get started, let’s get your toolkit ready. The good news is you likely have most of these items already. Having everything on hand makes the process smooth and quick.

Here’s your checklist:

Screwdriver: A Phillips head screwdriver is usually needed to remove the front cover of the unit.
Adjustable Wrench or Pliers: For loosening and tightening hose connections.
Bucket: To catch residual water from the filter and drain lines.
Garden Hose: A short, 5-10 foot hose is perfect for directing water from the drain valve to a floor drain or outside.
Air Compressor (Optional but Recommended): A small pancake or portable air compressor set to a low PSI (under 50 PSI) is a pro-level tool for ensuring every last drop of water is cleared from the heat exchanger.
Safety Glasses: Always protect your eyes when working on plumbing or mechanical systems.
Towels: For inevitable drips and cleanup.

The Complete Guide to Winterizing Your Navien Tankless Water Heater

Alright, with your tools gathered, it’s time to get to work. We’re going to walk through this step-by-step. The most important thing to understand is the difference between a long-term shutdown (draining the unit) and a short-term absence (relying on built-in protection). This winterizing navien tankless water heater guide covers both scenarios.

A Critical First Step: Understanding Your Situation

First, ask yourself: How long will the property be unheated and vacant?

Scenario 1: Long-Term Shutdown (e.g., closing a cabin for the winter). If the power will be off or the property will be vacant for weeks or months in freezing temperatures, you must perform a full drain-down. This is the only foolproof method.

Scenario 2: Short-Term Absence (e.g., a weekend trip). If you’ll be gone for a few days and the power and gas will remain on, you can likely rely on Navien’s excellent built-in freeze protection. We’ll cover the specifics for this in the next section.

This section focuses on Scenario 1: the full drain-down.

Step-by-Step: Draining Your Navien for Long-Term Shutdown

Don’t worry—this is straightforward. Just follow these steps in order, and you’ll be done in no time. This is how to winterizing navien tankless water heater units like a pro.

Safety First: Power and Gas OFF. This is the most important step. Go to your electrical panel and turn off the circuit breaker dedicated to your Navien unit. Next, find the gas shutoff valve on the gas line leading to the water heater and turn it to the “Off” position (the handle should be perpendicular to the pipe).
Shut Off the Water Supply. Locate the cold water inlet valve that supplies your Navien. It’s usually a red-handled valve (on the isolation valve kit) on the right side. Turn the handle so it’s perpendicular to the pipe to shut off the water.
Isolate the Unit. Now, do the same for the hot water outlet valve, which is typically a blue-handled valve on the left side. This isolates the water heater from your home’s plumbing system.
Open a Hot Water Faucet. Go to the nearest sink or tub and open a hot water faucet. You might get a trickle of water, but mostly you’ll just hear air. This relieves any pressure trapped in the hot water lines.
Connect Your Hose and Open Drain Valves. Look at your isolation valves again. You’ll see small T-shaped handles on the front. These are the drain ports. Unscrew the cap from the cold water side drain port, connect your garden hose, and place the other end in a bucket or floor drain. Now, open that T-handle by turning it.
Drain the Unit Completely. Water will now begin to drain out of the unit. To help it along, open the drain port on the hot water side as well. Next, locate the main pressure relief valve on the unit and lift the lever to allow air in, which helps the water drain faster. While it’s draining, locate the small, round filter cap on the cold water inlet connection. Place a towel underneath, unscrew it, and let the filter and any trapped water drain into your bucket.
Pro Tip: Blow Out the Lines. Once the water stops flowing, you can take an extra step for total protection. Using your air compressor with an appropriate fitting, introduce a low-pressure stream of air (keep it under 50 PSI to avoid damage) into the cold water drain port. This will push any stubborn, residual water out of the heat exchanger. You’ll be surprised how much more comes out!
Clean the Filter and Leave Valves Open. Clean any sediment off the inlet water filter before loosely reinstalling it. Leave the drain ports and the pressure relief valve lever open for the duration of the shutdown. This allows any condensation to escape and prevents a pressure buildup.

What About Short-Term Absences? Relying on Navien’s Built-in Freeze Protection

Navien units are smart. They come equipped with internal electric heating elements that automatically activate when the internal water temperature drops to a dangerous level, protecting the heat exchanger. This is a fantastic feature, but it comes with one massive, non-negotiable requirement.

For the built-in freeze protection to work, the unit must have a continuous supply of both electricity and gas.

If you lose power during a winter storm, the freeze protection system is useless. Therefore, you should only rely on this feature if:

You will be gone for a short period (a few days).
You are confident the power and gas supply will not be interrupted.
The unit is installed in a location that offers some protection from direct wind and extreme cold.

Even when relying on this feature, following winterizing navien tankless water heater best practices is wise. Ensure all exposed water pipes leading to and from the unit are well-insulated with foam pipe sleeves.

Common Problems and Mistakes to Avoid When Winterizing

Over the years, I’ve seen a few simple mistakes turn into big problems. By being aware of these, you can ensure your winterization process is flawless. These are the most common problems with winterizing navien tankless water heater procedures.

Forgetting to Turn Off the Power. If you drain the unit but forget to kill the power, the unit could try to fire up when it senses a call for heat. Firing a unit with no water in it (a “dry fire”) can cause immediate and severe damage to the heating elements.
Not Draining Completely. Just letting the water gravity-drain is good, but it can leave small pools of water in the coils. Using a bit of compressed air is the only way to be 100% certain every drop is out.
Over-Trusting the Built-in Protection. The most common failure I see is from homeowners who assumed the built-in system would work during a multi-day power outage in a blizzard. If power outages are common in your area, do not rely on this feature for protection.
Closing the Drain Valves After Draining. It feels tidy to close everything up, but this is a mistake. Leaving the drain valves open prevents any trapped moisture or condensation from being sealed inside, where it could potentially freeze.

Sustainable Winterizing: An Eco-Friendly Approach

Protecting your equipment can also be a green practice. A sustainable winterizing navien tankless water heater approach ensures you’re being mindful of resources while safeguarding your home.

The most significant eco-friendly aspect is the act itself. By preventing a catastrophic failure, you avoid the environmental impact of manufacturing and shipping a new unit and the waste of discarding the old one.

For a more eco-friendly winterizing navien tankless water heater process, consider these tips:

Capture and Reuse Water: When you drain the unit, capture the clean, potable water in a large bucket or watering can. Use it to water your houseplants or garden.
Choose Reusable Insulation: Opt for high-quality foam pipe insulation that can be used year after year instead of single-use materials.
Perform Regular Maintenance: A well-maintained unit is an efficient unit. Regular descaling and cleaning, as recommended by Navien, ensure it uses the least amount of energy possible when it is running.

Frequently Asked Questions About Winterizing a Navien Tankless Water Heater

Do I need to winterize my Navien if it’s installed inside my heated garage?

Generally, no. If the unit is in a conditioned or semi-conditioned space that is guaranteed to stay well above 32°F (0°C), you don’t need to drain it. However, if you plan to turn the heat off in your home or garage for an extended period, or if you are prone to long power outages that would cause the garage temperature to drop below freezing, then you absolutely should winterize it.

How cold does it have to be before I need to worry about my Navien freezing?

The danger zone begins with prolonged exposure to temperatures at or below 32°F (0°C). Navien’s internal freeze protection typically activates when the water temperature inside the unit drops to around 40°F (4.4°C). The real risk comes from extended periods below freezing, especially when combined with wind chill on exterior-mounted units, as this can overwhelm the built-in heaters.

I forgot to winterize and now I have no hot water. What should I do?

First, do not try to operate the unit. Immediately go and shut off the power at the circuit breaker and close the water supply valve leading to the heater. This prevents further damage if a frozen pipe thaws and begins to leak. Carefully inspect the unit and the surrounding pipes for any visible cracks, bulges, or drips. Do not apply direct, high heat (like a blow torch) to the unit or pipes, as this can cause them to burst. Your safest bet is to call a qualified, licensed technician to assess the situation.

Properly winterizing your Navien tankless water heater is a small investment of time that pays huge dividends in protection and peace of mind. By following these steps, you’re not just performing maintenance; you’re actively safeguarding one of your home’s most important systems from winter’s harshest effects.

You’ve got this. Stay warm and stay comfortable!

Author
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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.