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How to Descale Tankless Water Heaters: Step-by-Step Instructions

Wondering how to Descale Tankless Water Heaters? then you are at the right place.

A tankless water heater is a fantastic investment for your home, providing hot water on demand while saving energy and space. However, like any appliance, it requires regular maintenance to ensure optimal performance. One critical maintenance task is descaling your tankless water heater. In this comprehensive guide, we’ll walk you through the process step-by-step, explain why descaling is essential, and provide tips to help prolong the life of your unit.

What is Descaling and Why is it Important?

Descaling is the process of removing mineral buildup, or scale, from the heat exchanger of your tankless water heater. Minerals like calcium and magnesium are present in hard water and can accumulate inside the unit over time. This buildup reduces the efficiency of your heater, increases energy consumption, and shortens the lifespan of the appliance.

Signs that Your Tankless Water Heater Needs Descaling

There are several signs that your tankless water heater may need descaling:

  1. Reduced water flow: Scale buildup can clog the heat exchanger, restricting water flow and reducing efficiency.
  2. Fluctuating water temperature: Mineral buildup can interfere with the heat exchanger’s ability to heat water consistently.
  3. Noisy-operation: When scale accumulates, it can cause knocking, rumbling, or popping sounds during the operation.

If you experience any of these symptoms, it’s time to descale your tankless water heater.

Tools and Materials Needed for Descaling

To descale your tankless water heater, you’ll need the following tools and materials:

  1. Descaling solution: A commercial descaling solution or a mixture of white vinegar and water (1:1 ratio) can be used to dissolve the mineral deposits.
  2. Submersible pump: A pump is needed to circulate the descaling solution through the heater.
  3. Two five-gallon buckets: One for the descaling solution and one for the waste.
  4. Hoses: You’ll need two hoses, one for the inlet and one for the outlet.
  5. Gloves and safety goggles: To protect yourself during the process.

Step-by-Step Guide on How to Descale Your Tankless Water Heater

  1. Turn off the power: Make sure to turn off the power supply to your tankless water heater before starting the descaling process.
  2. Close the water valves: Turn off the cold water inlet and hot water outlet valves.
  3. Disconnect the electrical connectors: Remove any electrical connections between the heater and the water supply.
  4. Connect the hoses: Attach one hose to the cold water inlet and the other to the hot water outlet.
  5. Prepare the descaling solution: Fill one of the five-gallon buckets with the descaling solution or vinegar-water mixture.
  6. Set up the pump: Place the submersible pump in the bucket with the descaling solution and connect it to the hose attached to the cold water inlet.
  7. Begin the descaling process: Turn on the pump and let the solution circulate through the unit for at least 45 minutes.
  8. Flush the system: After descaling, remove the hoses, and open the cold water inlet valve to flush the unit with fresh water for 5 minutes.
  9. Reconnect the electrical connectors: Reattach any electrical connections between the heater and the water supply.
  10. Turn the power back on: Restore power to your tankless water heater.
  11. Test the unit: Turn on a hot water tap and allow the water to run for a few minutes, checking for any leaks and ensuring the water temperature is consistent.

Tips for Preventing Scale Buildup

To prolong the life of your tankless water heater and reduce the need for frequent descaling, follow these tips:

  1. Install a water softener: A water softener can help reduce the hardness of your water, thus minimizing scale buildup.
  2. Regular maintenance: Schedule annual maintenance with a professional to inspect and service your tankless water heater.
  3. Use a pre-filter: Installing a pre-filter on your water supply can help catch sediment and debris before it reaches your heater.
  4. Adjust the temperature: Lowering the temperature of your tankless water heater can help slow down the rate of scale buildup.


Descaling your tankless water heater is an essential maintenance task that can significantly improve the performance and extend the life of your unit. By following the steps in this comprehensive guide and implementing preventive measures, you can ensure your tankless water heater stays in peak condition for years to come. Remember, when in doubt, consult a professional to help you with the descaling process.

Frequently Asked Questions

How often should I descale my tankless water heater?

It’s recommended to descale your tankless water heater at least once a year, or more frequently if you have hard water.

Can I use CLR to descale my tankless water heater?

CLR can be used to descale your tankless water heater, but make sure to follow the manufacturer’s instructions and thoroughly flush the system afterward.

Is descaling a DIY job, or should I hire a professional?

Descaling your tankless water heater can be a DIY job if you feel comfortable and have the necessary tools. However, if you’re unsure or prefer a professional touch, it’s always best to hire a qualified technician.