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How to Descale A Noritz Tankless Water Heater (Demo)

Over time, all water heaters, be they storage tank- or tankless-type, inevitably build up scale deposits that can decrease their operating efficiency. The rate of scale build-up depends on a given geographic area’s water hardness, but sooner or later, it becomes appropriate to descale any unit. This blog will instruct you on how to a descale a Noritz tankless water heater.

To this end, Noritz has created a simple descaling procedure, outlined below. Although it’s possible for savvy homeowners to follow this themselves, a plumbing contractor should be brought in if there is any hesitation. For a visual explanation, view our video on How to Descale a Noritz Heater.

To descale a tankless water heater, you will need:

  • a five-gallon bucket;
  • three to four gallons of distilled, food-grade white vinegar;
  • two ¾ inch connection drain hoses;
  • a submersible pump.

Descaling a Noritz tankless water heater

Note Before Starting: On the unit, the red isolator valve indicates the hot water side, while the blue isolator valve indicates the cold water side. Drain caps are located on top of the hot side and on the left of the cold side. Turning the valves to the vertical position indicates they are “on” and that water is free flowing. Turning the valves to the perpendicular position indicates they are “off.”

1.  Keep the unit on but turn the gas valve off.

2.  Turn both hot and cold valves off. Remove the drain caps on both valves. Place the five-gallon bucket underneath the hot water side. Carefully turn the red drain valve to the “on” position and use the bucket to drain the unit of excess water still inside.

3.  Repeat step two on the cold water side.

4.  Connect a hose to the submersible pump and place the pump with the connected hose into the five-gallon bucket. Make sure the power cord stays out of the bucket.

5.  Connect the pump outlet hose to the cold water drain valve.

6.  Connect a drain hose to the hot water drain valve and place the end of the drain hose into the bucket.

7.  Pour between three and four gallons of vinegar into the bucket so that the pump is completely submerged. Open both drain valve lever handles on the 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. Eventually, an error code 11 will appear, which is normal during the procedure. DO NOT RESET.

8.  After a minimum of one hour, turn the pump off and close the cold water drain valve. Remove the hose from the cold water drain valve and replace the cap onto the drain valve outlet.

9.  Remove the pump and drain hose from the bucket and drain the liquid. Place the hot water drain hose back into the empty bucket and open the cold water main valve. This procedure will flush out the heater with fresh cold water. Flush for at least five minutes or until 20 gallons of water have passed through the heater.

10. For condensing units, place a bucket under the unit and twist open the drain cock located directly under the water heater to drain out any descaling medium that may have collected in the unit. Turn the main inlet valve to the “OFF” position.

11. For additional maintenance, unscrew and remove the water filter for cleaning—some water may flow out. 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.

12. 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.

13. Turn the main hot and cold valves back to the “ON” position and turn the gas supply back on. To get rid of the error code 11 that resulted from descaling, reset the unit by powering it off, then powering it on again.

See this descaling guide for more step-by-step information on the process.