Navien Tankless Water Heater Error Code 027 - Your Step-By-Step

There’s nothing quite like the jolt of an unexpectedly cold shower. You were counting on that steady stream of hot water, but instead, you’re met with an icy surprise and a cryptic message blinking on your Navien tankless water heater: Error Code 027.

It’s a frustrating moment, but don’t worry. This is a common issue, and you’ve come to the right place. We’re going to walk through this together, just like a technician would at your side.

We promise to demystify the navien tankless water heater error code 027, giving you a clear, safe, and actionable plan. This guide will help you understand what’s happening inside your unit, show you what you can safely check yourself, and clarify exactly when it’s time to call in a professional.

Let’s get that hot water flowing again. We’ll cover the causes, provide a step-by-step troubleshooting guide, and share some pro tips to prevent this from happening in the future.

What Does Navien Error Code 027 Actually Mean?

First things first, let’s translate that code. In the world of Navien tankless water heaters, Error Code 027 points directly to a problem with the condensate drain line.

Essentially, your high-efficiency Navien unit is telling you, “Hey, I can’t get rid of my wastewater, so I’m shutting down for safety!”

High-efficiency tankless water heaters like Navien’s work so well because they capture extra heat from the exhaust gases. As these gases cool down, they create condensation—a small amount of acidic water. This is a normal and expected byproduct of the process. Your unit is designed to collect this condensate and safely drain it away through a small tube, usually made of PVC or vinyl.

When that drain line gets blocked, kinked, or frozen, the water backs up. A sensor inside the unit detects the high water level and triggers Error Code 027, shutting the heater down to prevent water from overflowing and damaging internal components. It’s a smart safety feature, but it leaves you without hot water.

Unpacking the Common Problems with Navien Tankless Water Heater Error Code 027

So, what’s causing the blockage? The issue almost always lies somewhere along that small drain path. Here are the most common culprits we see in the field.

The Clogged Condensate Drain Line

Over time, small bits of debris, sediment from the combustion process, or even algae can build up inside the condensate trap and drain line. This gunk can create a stubborn clog, preventing water from flowing freely. It’s the most frequent cause of Error 027, especially in units that haven’t had regular maintenance.

A Frozen Condensate Line (A Winter Culprit)

If your drain line terminates outside your home, it’s extremely vulnerable to freezing temperatures. During a cold snap, the slow trickle of condensate can easily turn into an ice plug right at the end of the pipe, causing a complete blockage. If your hot water goes out on the coldest day of the year, a frozen line is the prime suspect.

Improper Installation or Pitch

This is less common, but it happens. For gravity to do its job, the condensate drain line must have a consistent downward slope (or “pitch”) from the unit to the termination point. If the line is installed perfectly flat or, even worse, runs uphill at any point, water will pool and eventually back up, triggering the error.

A Faulty Component

In rare cases, the problem might not be a blockage at all. The sensor that detects the water level could be malfunctioning, or the internal condensate trap could be damaged. These issues are much harder to diagnose without professional tools and are a clear sign it’s time to call a technician.

Your Safe, Step-by-Step Navien Tankless Water Heater Error Code 027 Guide

Alright, let’s get hands-on. Here are a few safe checks you can perform to identify and potentially resolve the issue. This how to navien tankless water heater error code 027 section will empower you to tackle the basics.

IMPORTANT SAFETY WARNING: Before you begin, you must turn off the electrical power to your water heater at the circuit breaker. For added safety, you can also shut off the gas supply valve leading to the unit. Your safety is always the top priority.

Step 1: Visually Inspect the Condensate Drain Line
Start by locating the drain line. It’s typically a small, flexible vinyl tube or a white PVC pipe coming from the bottom of your Navien unit. Follow its entire path, from the heater to where it drains (a floor drain, utility sink, or outside).
Look for any obvious problems:
- Is the tube sharply kinked or pinched?
- Is it crushed under something?
- Can you see a visible blockage or buildup of gunk?
Sometimes, simply straightening out a kink is all it takes to solve the problem.
Step 2: Check for a Frozen Line (If It’s Cold Outside)
If the temperature is near or below freezing and your line terminates outdoors, feel the end of the pipe. If it feels icy or you can see ice plugging the opening, you’ve likely found your culprit.
To safely thaw it, use a hairdryer on a low to medium setting or wrap the pipe in warm, damp cloths. Never use an open flame like a torch or lighter, as this can melt the pipe and create a serious fire hazard.
Step 3: Clear the Condensate Trap and Line
If you don’t find an obvious external blockage, the clog is likely inside the line or the unit’s internal trap. Your Navien’s user manual will show the exact location of the condensate trap.
Carefully disconnect the drain tube from the unit’s connection point. Have a small bucket or towel ready, as some water will spill out. Once disconnected, you can try to clear the line by blowing through it or using a wet/dry vacuum on the end to suck out the blockage. For a more thorough cleaning, you can flush the tube with a warm 50/50 solution of water and white vinegar to dissolve mineral buildup.
Step 4: Reset Your Navien Unit
After you’ve cleared the blockage and reconnected the drain line securely, it’s time to restore power at the circuit breaker. Once the unit boots up, the error code should be gone. If your model has a reset button, you may need to press it. Run a hot water tap for a few minutes to confirm everything is working correctly.

Navien Tankless Water Heater Error Code 027 Best Practices for Prevention

Fixing a problem is good, but preventing it is even better. Adopting a few best practices will dramatically reduce the chances of seeing Error 027 again. This is your long-term navien tankless water heater error code 027 care guide.

The Importance of Annual Maintenance

This is the single most effective thing you can do. During an annual service call, a qualified technician will descale your unit to remove mineral buildup and will thoroughly clean the entire condensate drainage system—including the internal trap and the full length of the drain line. This professional cleaning removes gunk before it can become a major clog.

Insulate Your Exterior Drain Line

If you live in a climate with freezing winters, this is a non-negotiable tip. Ask your HVAC technician to insulate the exterior portion of your condensate line with foam pipe insulation. It’s a simple, low-cost upgrade that provides excellent protection against ice blockages.

Regular Flushing for an Eco-Friendly and Sustainable System

For the proactive homeowner, a quarterly flush of the condensate line is a great DIY task. Simply pour a cup of a 50/50 white vinegar and water solution into the condensate collector (as shown in your manual) to help break down any early-stage buildup. A clean, well-maintained system runs more efficiently, making this an excellent eco-friendly navien tankless water heater error code 027 prevention tip that also promotes a more sustainable operation by extending the unit’s lifespan.

When DIY Isn’t Enough: Knowing When to Call a Professional

While many Error 027 issues are fixable, it’s crucial to know your limits. Your safety and the health of your expensive equipment are paramount.

You should call a licensed and insured HVAC or plumbing professional if:

The error code returns immediately after you reset the unit.
You are uncomfortable or unsure about performing any of the troubleshooting steps.
You suspect the drain line is clogged deep inside a wall or is otherwise inaccessible.
You have cleared the line, but the error persists (this could indicate a faulty sensor).
You notice any water leaking from the main casing of the water heater itself.

Frequently Asked Questions About Navien Error Code 027

Can I just keep resetting my Navien heater if I get error code 027?

No, this is not a good idea. The error code is a safety alert. Continuously resetting it without addressing the underlying blockage can cause water to back up into the unit, potentially damaging sensitive electronics or even the heat exchanger, leading to much more expensive repairs.

How much does it cost to fix a Navien error code 027?

The cost can vary widely. If it’s a simple clog that a homeowner can clear, the cost is virtually zero. If you need a professional service call, you can expect to pay a standard diagnostic fee plus labor. For a straightforward drain line cleaning, this might be $100-$250. If a part like a sensor needs replacing, the cost will be higher.

Is the water from the condensate line dangerous?

The condensate is mildly acidic, with a pH similar to soda or vinegar. While it’s not highly corrosive, you should avoid getting it on your skin and wash your hands after handling the drain line. It’s important that it drains into a suitable receptacle, like a utility sink or a floor drain with a neutralizer kit, not onto your lawn or a finished surface.

Will my Navien work with a clogged condensate line?

No. The unit’s internal logic is designed to shut down all heating operations when Error Code 027 is active. This is a protective measure to prevent internal water damage. Your unit will not produce hot water until the blockage is cleared and the system is reset.

Tackling an error code can feel daunting, but you’ve just walked through the exact process a pro would. By understanding what Error 027 means and following these safe, logical steps, you are now equipped with the knowledge to handle it confidently.

Remember that regular maintenance is the key to reliability. A little preventative care goes a long way in ensuring you have consistent, efficient hot water when you need it most. Stay safe, and enjoy that hot shower!

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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.