Over time, all storage water heaters, whether tank or tankless, eventually build up deposits that can decrease their performance. The quicker a scale builds up, the harder it is to clean. It doesn’t matter if the water hardness is low or high. This blog was written as a guide to descale a Noritz tankless water heater.

So that I don’t get my writing skills rusty, I’ve created a simple descaling procedure. Although it is possible for savvy homeowners to follow this procedure themselves, it is not a good idea for all types of bathroom surfaces. A plumber should be called in if there are doubts. For a visual explanation, view our video on How to Descale a Noritz Heater.

Descale  Noritz Tankless Water Heater, you will need:

  1. A five-gallon bucket;
  2. Three to four gallons of distilled, food-grade white vinegar;
  3. Two ¾ inch connection drain hoses;
  4. A submersible pump.


Note: On the unit, the red isolator valve indicates the hot water side, while the blue isolator valve indicates the cold water side. Water valves are located on top of the hot side and on the left of the cold side. To indicate that water is free flowing, the valves are turned to the vertical position. Turning the valves off means they are working and ready to receive water.

  1. Keep the water heater on and the gas valve off.
  2. Turn off both hot and cold water at the same time. Remove the hot water valve cap. Place the five-gallon bucket underneath the cold water side. When you turn the red valve to the “on” position, use the bucket to drain the unit of excess water still inside.
  3. .Repeat step 2 on the cold water side.
  4. .Connect a filter with a hose to the submersible pump. Place the pump with the attached hose into the five-gallon bucket.
  5. Connect the pump outlet hose to the cold water drain.
  6. Connect a hose to the hot water drain valve and place the end of the hose into the bucket.

  7.  Pour three to four gallons of vinegar into the bucket so that the pump is completely submerged.    Open both isolation valves and turn on the pump for at least an hour. For maximum effectiveness, change the vinegar solution after 30 minutes and repeat. The unit will try to fire up, but will fail due to the gas being off.   Finally, you will find the error code 11. It’s normal during the process. Don’t reset it.
  8. After at least a one-hour time, turn the pump off and close the cold water drain valve. Remove the hose from the cold water drain valve and replace it on its original position.
  9.  Remove the bucket and hose from the pump and drain the liquid. Place back into the empty bucket and open the cold water main valve.   This will flush out the heater with fresh cold water. Flush for at least 5 minutes or until 20 gallons of water have passed through the heater.  
  10. For condensing units, have a bucket underneath and twist open the drain cock located under the water heater to drain out any descaling medium.    

Read; How to Flush a Noritz Tankless Water Heater in 14 Easy Steps

  1. .For additional maintenance, unscrew and remove the water filter for cleaning—some water may flow out.  To prevent corrosion, it’s important to clean the housing every two weeks and the flush valve every six months.  Clean the filter under running water to remove any debris. Place the dry filter back into the port, making sure it’s twisted tightly by hand.  To clean the filter properly, you need to run it over a sink for about 30 seconds. After that, you need to clean out any residue and debris from inside the filter by running it under running water. The filter needs to be clean and clear of any dirt, before you reinstall it.  
  2. Turn the drain valve to the “OFF” position. Unscrew and remove the drain hose. Replace the drain cap and make sure it’s screwed on tightly.  Unscrew the cap, remove the drain hose, and replace the cap.  
  3. Turn the main hot and cold valves back to the “ON” position and turn the gas supply back on.  Turn the main hot and cold valves back to the “ON” position and turn the gas supply back on.    To remove the error code 11 that resulted from descaling, power off the unit and then power it on again.  

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