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Flushing your tankless water heater

Flushing your tankless water heater

Flushing your tankless water heater

Two of the biggest questions we hear: How often should you flush your tankless water heater and how do I flush my tankless water heater. Because your tankless water heater burns at much higher BTU’s it will require maintenance to keep it operating at its peak potential. The longer you go the more likely it is to work less efficiently, provide less hot water and potentially damage the internal components of your tankless water heater. With routine yearly maintenance, you will have a happy tankless water heater and take long enjoyable showers. Here are some of the benefits of regular tankless maintenance.


  • Meets heat exchanger warranty requirements
  • Prevents limescale build up
  • Delivers maximum amount of hot water
  • Keeps heat exchanger cool preventing damage
  • Runs at the highest efficiency level
  • Extends the life of your tankless investment


Things You Will Need

Screwdriver, Non-contact electrical tester, Bucket, 5-gallon Pond pump or small sump pump (or designed tankless flush pump kit), 2 sections of garden hose with connectors, Minimum 6-foot-long, Adjustable wrench, 5 gallons of white vinegar or 1 quart of flow aid.

* Your tankless water heater must be equipped with a bypass kit (isolation valves) to allow the option to close and bypass the entire home plumbing system. Thus, only cleaning the tankless water heater.



Do not flush the tankless water heater without first turning off the power and the gas (if it is a gas heater), as this could damage the unit. Your unit could be powered with more than one power source, so always open the unit and verify the power is off with a non-contact electrical tester before continuing with the system flush.

Failure to turn off all power sources when flushing could cause damage to the unit.


Directions (based on tankless manufactures recommendations).

  1. Turn the power OFF (electricity and gas) to your tankless heater.
  2. Close the shutoff valves on hot and cold-water lines.
  3. Use the service (isolation) valve and connect the Flow-aide system to the cold-water line (garden hose is OK). The circulation pump within the flow-aide system is used to force the flushing solution through the heater.
  4. Now connect the heater with the hose, by using another service valve and terminate it to the appropriate drain bucket.
  5. Drain hose and pump hose should end in the same bucket as the flow-aide system.
  6. Open both service valves.
  7. Run the circulation pump and let the flushing solution go through the unit for one hour approximately.
  8. Turn the pump OFF.
  9. Rinse the cleaning solution from the water heater by opening the shutoff valve on the cold-water line (close the service valve between the pump and the heater) so it runs through the heater and into the bucket (approximately 5 mins.) After that open the shutoff valve on the unit and close the service valve between the heater and the bucket.
  10. Disconnect all hoses.
  11. The recommendation is also to clean the in-line filter.
  12. Resume the power and run the water heater.
  13. Check the hot side of all plumbing fixtures to confirm hot water to all locations, it’s a good idea to clean the aerators on each faucet currently as well.

For more information regarding flushing your tankless water heater check out this quick tankless video…