How to Clean a Hot Tank

On a StandUp Oasis Bottled Water Cooler with Non-removable Reservoir
Water cooler hot tanks need to be cleaned periodically to prevent mineral build-up inside the heating tank. The frequency of cleaning is determined by the quantity of minerals in the water and the amount of water used. To extend the amount of time before cleanings use our ‘Best’ level filters. They can drastically reduce hard water mineral buildup, thus greatly extending the time before the hot tank needs to be cleaned again.

Water cooler heating tanks may require cleaning when:

  • Normal hot water flow appears restricted.
  • Noisy heating cycles are heard.
  • Water in the cooling reservoir is very warm.
  • The water tastes bad due to mineral build up. (On a bottleless cooler this can also mean you need new filters.)

Tools Caution: Because this cleaning process involves very hot water that may scald, the use of rubber gloves is recommended. KEEP CHILDREN AWAY DURING CLEANING PROCESS.
Before you start, you’ll need the following:

  1. 4 ounces (113 grams) of citric acid crystals. Your local drug store or grocery should have this.
  2. Clean rubber gloves
  3. Clean container that can hold 2 gallon or more
  4. One 1/4” (7mm) socket wrench.
  5. A funnel with a 1/2” (13mm) diameter at the end.
  6. A quart measuring container for hot liquids.


  1. Disconnect power cord of the water cooler from the wall outlet.
  2. Draw water from the hot water faucet until the water is cool.
  3. Remove the bottle from the water cooler.
  4. Remove the plastic baffle.
  5. Drain the hot tank. Most Oasis water coolers have a drain tube that leads to a plug in the back of the unit, others have a valve or cap.
  6. Drain all the water remaining in the cooling tank of the water cooler through the cold faucet.
  7. Replace drain tube cap, plug or close its valve.
  8. Mix 4 ounces of citric acid crystals with one quart of very hot water. (Wearing rubber gloves is recommended.)
  9. Place a funnel inside the cooling tank at the center fitting. Carefully pour the hot solution into the funnel. Be careful not to scald your hands!
  10. Remove the funnel and fill the cooling tank of the water cooler with bottled water until the water level is about 3” (76mm) from the top. To allow the hot tank to fill, open the hot faucet until water begins to flow, then close the faucet.
  11. Plug the power cord of the water cooler back in to the wall outlet.
  12. Let the water cooler unit stand for at least twenty minutes.
  13. Unplug the power cord of the water cooler again.
  14. Using rubber gloves and being cautious of water that may scald, draw water from the hot faucet of the water cooler until the flow ceases. Open the heating tank drain catching the water in a pan or bucket. The water will be discolored. Note: This drain water should be immediately poured down a drain to prevent accidental spilling; this water will stain.
  15. Pour at least 1 gallon of bottled water into the water cooler cooling reservoir and allow this water to drain out the heating tank drain. Drain all remaining water from the water cooler cooling tank through the cold faucet.
  16. Replace cap or plug or turn the drain valve to a closed position when the tank is empty.
  17. Replace the top bottle ring or gasket and receptor.
  18. Replace the baffle and place a bottle of water on the water cooler. Open the hot faucet to allow the hot tank to fill.
  19. Plug the power cord of the water cooler back in to wall outlet.
  20. After the water cooler has run for ten to fifteen minutes, draw at least one quart of water from each hot and cold faucet.

Your water cooler’s heating tank should now be clean. If the flow of water or the noisy heating cycles do not improve, you should have the unit repaired at an authorized service center.

If you have any questions about any of the above, feel free to give us a call at 1-800-390-6132.