In the video, Brian flushes a Navien tankless water heater with white vinegar, using hoses connected to the unit's service valves. Flushing removes mineral scale that can clog the heat exchanger.

Video by Brian Huie on YouTube. Watch on YouTube

How often: Every 18 to 24 months (Brian's schedule)
Video: 1 min 36 sec

How often should a tankless water heater be flushed?

Brian's schedule is every 18 to 24 months. Navien ties the interval to water hardness: its installation manual lists no required flushing for soft water (0 to 4 grains per gallon) and once a year for moderately hard or hard water, while its blog suggests at least once a year. Harder water, higher temperatures and heavier use all mean flushing more often.

Why does it matter?

Navien says mineral buildup can erode and clog the inside of the heat exchanger, reducing efficiency and leading to early failure.

How is it done? (Navien pump-and-bucket method)

Turn the heater off, disconnect power and close the gas valve.
Close the hot and cold isolation valves.
Connect hoses to the service valves, with a small circulation pump drawing from a 5-gallon bucket.
Pour white vinegar or a descaler made for tankless heaters into the bucket and circulate it for at least 45 minutes.
Rinse with fresh water (5 minutes per the manual), then clean the cold water inlet filter, reassemble and restore power.

Safety notes

Navien says descaling takes at least basic experience with plumbing tools, plus equipment such as a submersible pump and drain hoses. Follow all safety directions on the descaling product.
If you smell gas, do not touch switches or appliances; leave and call the gas supplier from a neighbor's phone.

Seattle-area notes

Seattle's water is soft. Seattle Public Utilities measured 0.5 to 1.73 grains per gallon in May 2026, which falls in Navien's soft range. Homes on a well or another utility should check their own water report.

When to call a pro

Navien recommends hiring a professional to descale, and warns that damage from descaling done incorrectly could void the warranty.

Sources

Checked October 2026. Manufacturer instructions for a specific model come first. General information, not a substitute for a licensed professional.

From the Home Care Advice by Brian Huie, a principal broker and Realtor with Compass in Seattle.

Home Care Advice

How to flush a tankless water heater