How to Flush Your Navien Tankless Water Heater (Minneapolis Homeowners Guide)

If you own a Navien tankless water heater in the Minneapolis area, keeping it clean is just as important as owning it. These high-efficiency systems provide endless hot water, but they need regular care to keep working the way they should. That includes flushing or descaling the unit once a year.

In this post, we’ll walk you through why flushing matters, how to do it safely, and when to call a licensed plumber.

Why You Need to Flush a Tankless Water Heater

A step-by-step guide for Minneapolis homeowners on how to flush a Navien tankless water heater. Keep your unit running efficiently with this simple yearly maintenance routine.

Over time, minerals in Minnesota’s hard water build up inside the unit’s heat exchanger. This buildup, called scale, can block water flow and reduce heating efficiency. If left unchecked, it can even damage the unit and cause system errors.

Flushing removes that scale and keeps your Navien working properly. It also helps:

• Improve hot water speed and pressure

• Lower your energy bills

• Extend the life of your water heater

How Often Should You Flush It?

Most homeowners in the Twin Cities should flush their Navien once per year. If you have especially hard water or use a lot of hot water, you might need to do it every 6 months.

What You’ll Need

• A 5-gallon bucket

• White vinegar or tankless water heater descaler

• A submersible pump

• Two washing machine hoses

• Towels and gloves

• Access to the unit’s hot and cold service valves

Step-by-Step Flushing Instructions

Caution: Only do this if you're comfortable handling basic plumbing and have isolation valves installed.

1. Turn Off Power and Gas

Shut down the unit using the power button, then unplug it or turn off the breaker. Close the gas valve.

2. Shut Off the Water Lines

Close both the cold and hot water valves going into the unit.

3. Hook Up Your Flush Kit

• Connect one hose from the pump to the cold water service port

• Connect another hose from the hot water service port into your bucket

• Pour vinegar or descaler into the bucket (usually 4 gallons)

4. Circulate the Cleaner

Turn on the pump and let the vinegar run through the unit for 45 minutes. This breaks down mineral scale.

5. Flush with Fresh Water

Once done, remove the vinegar. Open the cold water valve briefly to flush clean water through the system and rinse it out.

6. Clean the Inlet Filter

Unscrew and rinse the cold-water filter screen to remove any leftover debris.

7. Restore Water, Gas, and Power

Close all service valves. Open the main hot and cold valves. Restore power and gas. Check that hot water is running.

Signs Your Navien Needs Flushing

• Water takes longer to heat

• You hear strange sounds from the unit

• You get an error code (like E110)

• Your monthly energy bill goes up

Don’t Want to Do It Yourself?

Flushing a tankless unit is doable, but not always simple. If you don’t have the right valves, tools, or time, it’s safer to call a licensed plumber.

At Predictable Plumbing, we offer flat-rate Navien water heater maintenance for homes in:

• Minnetonka

• Wayzata

• Plymouth

• St. Louis Park

• Hopkins and nearby areas

We’ll flush your system, clean the filter, check for error codes, and make sure your Navien keeps working like it should.

Need help with your Navien? Call Predictable Plumbing or book online in 60 seconds.