Navien Tankless Flush: What To Do (And Avoid)

If your Navien tankless takes too long to deliver hot water, yearly maintenance can help. A careful flush and filter clean keeps the heat exchanger efficient and prevents surprises.

What you’ll get:

• Simple yearly flush steps
• Filter cleaning order that avoids messes
• A safe recirculation setup with vinegar
• Hard-earned tips to prevent a geyser

Prep: Power, gas, and water off

• Turn the unit off, unplug it, and close the gas valve.
• Close both hot and cold water valves. Remove the front cover only if you must; the unit may not power on without it installed.
• Have an extension cord ready if your pump can’t reach an outlet.

Clean the filters first

• Top cold-air intake screen: check and vacuum if accessible; indoor installs often stay clean.
• Under the unit: remove and clean the cold water inlet filter, then the dirt trap. Do this before circulating vinegar so debris doesn’t foul the pump.
• Drain the system at the service ports to reduce mess before pulling filters.

Set up the vinegar recirculation

• Connect washing machine hoses to the service ports: vinegar in through cold, out through hot.
• Submerge the 1/6hp sump pump in a bucket with white vinegar (about 2 gallons). Keep hose connections tight and pointed into the bucket before plugging in the pump—this is where geysers happen.
• Run the pump for 40–45 minutes. Expect light discoloration early on; continue the loop regardless so the exchanger is fully bathed.

Button up without drama

• Power down the pump, remove hoses, and close service ports. Reopen the hot and cold water valves.
• Let components dry if anything got wet. Don’t rush power-up.
• Reinstall the front cover before attempting to turn the unit back on; some units won’t start without it in place.

Final takeaway: A careful filter clean plus a controlled vinegar loop is the yearly baseline. Work methodically, keep the cover on unless necessary, and if anything feels beyond your comfort level, call a plumber.