How to Descale Rinnai Water Heaters

Rinnai offers a line of tankless water heaters, which warm the water as you use it.
Have a professional service the appliance annually.Have a professional service the appliance annually.
Despite its lack of a large water tank, this type of water heater can still become clogged with mineral deposits. Descale the water heater periodically to improve its performance. Flush the unit with white vinegar. The directions for descaling may vary slightly, depending on the specific model you have. When in doubt, refer to the owner's manual or contact Rinnai.

Step 1

Turn off the water heater and close both of the shutoff valves.

Step 2

Attach the pump outlet hose to the cold water line. Attach the drain hose to the service valve. Place the other ends of both hoses into a 5-gallon bucket.

Step 3

Pour 4 gallons of distilled white vinegar into the bucket.

Step 4

Open both of the service valves and turn on the pump. Wait one hour for the vinegar to circulate in the water heater and remove the mineral buildup. Turn off the pump.

Step 5

Remove the drain hose from the pail. Only remove the hose that's connected to the service valve, not the hose that's connected to the cold water line. Keep the other end of the drain hose connected to the service valve.

Step 6

Close the service valve that's connected to the cold water line. Open the shutoff valve connected to the cold water line. Let the water circulate for five minutes.

Step 7

Close the service valve that's connected to the hot water line. Open the hot water line shutoff valve.

Step 8

Remove both of the hoses from the hot water heater.

Step 9

Close the cold water line shutoff valve and remove the cold water in-line filter. Rinse the filter to remove mineral buildup and replace it. Open the cold water line shutoff valve.

Step 10

Turn the water heater's electrical power on.

Things You Will Need

  • 5-gallon bucket
  • 4 gallons white vinegar

About the Author

Catherine Chase is a professional writer specializing in history and health topics. Chase also covers finance, home improvement and gardening topics. She holds a Bachelor of Arts in American studies from Skidmore College.