How to Flush Your Navien Tankless Water Heater (Minneapolis Homeowners Guide)
- Predictable Plumbing
- Jun 11, 2025
- 4 min read
Updated: Dec 16, 2025
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
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:Â 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 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
(For units with recirculation) Connect a third hose to the recirculation outlet on the water heater, and place the free end into the bucket.
Pour cleaning vinegar or pour a manufacturer approved tankless water heater descale product into the bucket, typically about 4 gallons.
4. Circulate the Cleaner
Turn on the pump and let the product run through the unit for 45 minutes. This breaks down mineral scale.
5. Flush with Fresh Water
Once done, remove the cleaning solution. Open the cold water valve, leaving the hot service valves open to flush clean water through the system and rinse it out. Allow water to flow through the unit in through the cold side, and out through the hot service port, into a nearby drain.
6. Clean the Inlet Filter
Unscrew and rinse the cold-water inlet filter screen to remove any leftover debris. For A models with recirculation, remove and clean the recirculation inlet filter as well.
Clean air inlet filter
The unit has an air intake and an exhaust labeled on the top of the unit. With the units cover removed, locate the air intake. Remove the screw securing the air intake filter on the top left of the heater. Remove and clean the filter using a soft brush and water. Allow filter to dry before placing it back into the unit.
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.
Navien Tankless Water Heater Flushing FAQ
Is flushing a Navien tankless water heater required?
Navien recommends regular flushing as part of routine maintenance. In areas with hard water like Minnesota, annual flushing helps prevent scale buildup and error codes.
Can skipping flushing damage a Navien unit?
Yes. Scale buildup can restrict water flow, reduce efficiency, and shorten the life of the heat exchanger.
Does flushing affect the Navien warranty?
Lack of maintenance can affect warranty coverage. Keeping records of annual flushing helps protect warranty claims.
Can I flush a Navien without service valves?
No. Isolation valves are required to flush the unit safely. If they are not installed, a plumber should add them first.
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:
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.