How To Flush A Noritz Tankless Water Heater: Step-by-Step Guide

Flushing your Noritz tankless water heater regularly is an important part of maintaining your system. By learning how to flush a tankless water heater, you can ensure that it is working properly and efficiently for years to come. In this guide, we’ll walk you through the process of flushing a Noritz tankless water heater so that you can do it yourself.

Flushing A Noritz Tankless Water Heater

Flushing your Noritz Tankless Water Heater is a relatively straightforward process, however, it does require materials and tools to complete the job. Make sure that you have the required materials and tools to complete the job before starting. If you need help, schedule an appointment with the licensed plumbers at Payless Water Heaters!

Materials Needed

  • 5-gallon bucket
  • 4 gallons of distilled white vinegar
  • 2 drain hoses, ¾ inch
  • Submersible pump

Step-by-Step Descaling and Flushing a Noritz Tankless Water Heater

  1. Keep power to your Noritz tankless water heater but turn off the gas supply valve.
  2. Turn off the hot (red) and cold (blue) water supply valves. There should be drain caps on both valves where the water will drain through. Remove these caps.
  3. Under the hot water valve, place a bucket to catch the water. A 5-gallon bucket is fine. Turn the hot water valve on and allow your Noritz unit to drain all of the water still left inside. Turn the valve back off once the water has finished draining.
  4. Repeat the process in the step above for the cold water valve. You may need to empty your 5-gallon bucket before starting this step.
  5. Empty your bucket again before starting this step. Connect a hose to the submersible pump outlet and place the pump in the bucket. Position it so that you keep the power cord out of the bucket.
  6. Connect the other end of the hose to the cold water drain valve. Connect the second hose to the hot water drain valve with the other end draining into the bucket.
  7. Pour enough vinegar into the bucket so your pump is completely submerged. If it isn’t submerged, it will not work properly and could overheat. At this point, you can open the hot and cold water valves. Once the valves are open, turn the pump on and leave it running for at least one hour. At the 30-minute mark, you can pause the process by turning off the pump, shutting off the valves, and then changing out the vinegar if you notice it is recirculating dirty vinegar.
  8. NOTE: The unit will try to fire up. However, because you turned the gas off, it will fail. Your tankless water heater may give you error code 11, however, you should NOT reset it. This is normal.
  9. You can repeat step 7 as many times as needed until your tankless water heater is clean.
  10. Once your Noritz tankless water heater is flushed, descaled, and clean, you can turn the pump off and shut off both drain valves. Remove the hose from the cold water drain valve and replace the cap you took off in step 2. Empty your 5-gallon bucket.
  11. With the hot water drain valve still connected to the drain hose leading to an empty bucket, open the cold water supply valve. This will allow cold water to flush out the water heater. Allow this process to go on until your bucket is nearly filled with water. Turn off the cold water supply valve and empty the bucket. Repeat this process 3 more times.
  12. Turn off the cold water supply valve, close the hot water drain valve, and remove the drain hose from the hot water drain valve. Replace the hot water drain valve cap that you removed in step 2.
  13. Turn the main hot and cold water valves back on and turn the gas supply back on. Reset your Noritz tankless water heater by powering it off and then powering it back on again to clear error code 11.

It’s important to note that if you notice any unusual sounds coming from either hot or cold valves during flushing then stop immediately as this could indicate a problem with your system that requires professional attention.


Flushing a Noritz Tankless Water Heater doesn’t need to be difficult or risky if done correctly; just be mindful of the process provided above. Following these steps should help you flush any sediment buildup from your Noritz Tankless Water Heater easily and quickly so that it runs efficiently and effectively for years to come. Call Payless Water Heaters if you need help maintaining or repairing your Noritz tankless water heater, and don’t forget to check out our reviews!