The Ultimate Guide to Flushing Tankless Water Heaters!

Flushing tankless water heaters is essential for maintenance, and our guide makes it simple.

Learn when and how to effectively flush your unit to maintain top performance, ensure efficient heating, and extend its lifespan by removing limescale and sediment buildup.

By incorporating this crucial step into your routine, you can avoid costly repairs and enjoy uninterrupted hot water. Our step-by-step guide demystifies the process, making it accessible for homeowners to achieve professional results.

Understanding the unique design of tankless water heaters is key. Unlike their tank-type counterparts, they do not store hot water. Instead, they heat cold water on demand through a heat exchanger.

This heat exchanger, positioned typically underneath, is heated by a gas burner. It features a series of water pipes and numerous thin fins to optimize heat transfer.

With this understanding, the importance of regular maintenance to maintain the system's efficiency and extend its lifespan becomes clear.

Benefits of flushing tankless water heaters

Rinnai tankless water heaterRinnai tankless water heater

Flushing your tankless water heater regularly offers several significant benefits that can improve performance, extend the unit's lifespan, and provide cost savings. Here are some of the key benefits:

Improved Efficiency: Over time, mineral deposits from hard water can accumulate in the heat exchanger and other parts of your water heater, reducing its efficiency. Flushing these deposits out helps to maintain optimal operation, ensuring that the heater can quickly and efficiently heat water, which can lead to energy savings.

Extended Lifespan: Regular flushing can significantly extend the lifespan of your tankless water heater. By removing mineral buildup, you reduce the stress on the heater's components, preventing premature wear and tear. This can save you money in the long run by delaying the need for a replacement.

Consistent Water Temperature: Sediment and scale buildup can cause fluctuating water temperatures, including unexpected hot water outages. Regular flushing helps maintain consistent water heating performance, ensuring you always have access to hot water when you need it.

Prevention of Costly Repairs: Mineral buildup can lead to overheating and damage to the heat exchanger, one of the most critical and expensive components of your tankless water heater. Regular flushing can prevent these issues, avoiding costly repairs and replacement parts.

Energy Cost Savings: A tankless water heater that operates efficiently consumes less energy. By maintaining a clean system through flushing, you ensure that the heater operates at peak efficiency, which can lead to lower energy bills.

Better Water Quality: Flushing out sediment and mineral deposits not only improves the efficiency and lifespan of your heater but also contributes to better water quality. This can enhance your overall home water usage experience, ensuring that the water is clean and free of any potential buildup that could affect taste or health.

Maintains Warranty Coverage: Many tankless water heater manufacturers require regular maintenance, including flushing, as part of the warranty terms. By adhering to these requirements, you ensure that your warranty remains valid, providing peace of mind and protection against potential defects or malfunctions.

Environmental Benefits: Tankless water heaters are already more energy-efficient than traditional tank heaters, but maintaining that efficiency through regular flushing means less energy consumption overall. This contributes to lower carbon emissions and a smaller environmental footprint.

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Required tools

  • Adjustable wrench
  • Plumber wrench
  • Screwdriver
  • Multimeter
  • Bucket
  • Small submersible pump
  • Garden hose (2 pieces) (or a kit)

Instructions on how to flush a tankless water heater

As said, flushing a tankless water heater is not complicated, and once done correctly, you have to reset the fault code by resetting the power. Here are the step-by-step instructions (I will consider that isolation or service valves are installed):

  • Turn off the power (both electricity and gas) to your tankless heater.
  • Close the valves on both hot and cold water lines.
  • Use the service (isolation) valve to connect the circulation pump (such as a pond pump) to the cold water line (a garden hose is acceptable). The circulation pump is used to force the flushing solution through the heater. To make the flushing solution, use approximately 4 gallons of food-grade white vinegar. Alternatively, you can buy a descaler from the tankless manufacturer. It is recommended to use a non-toxic, non-corrosive, and biodegradable cleaning solution.
  • Pour the cleaning solution (vinegar or descaler) into the bucket.
  • Connect the hose to the heater using another service valve and direct it to the appropriate drain bucket.
  • The drain and pump hoses should both end in the same bucket and be immersed in the cleaning solution.
  • Open both service valves on the hot and cold water lines.
  • Run the circulation pump and allow the flushing solution to circulate through the unit for approximately one hour.
  • Turn the pump OFF.
  • Rinse the cleaning solution from the water heater by opening the shutoff valve on the cold water line (close the service valve between the pump and heater) so it runs through the heater and into the bucket (for approximately 5 minutes). After that, open the shutoff valve on the unit and close the service valve between the heater and the bucket.
  • Disconnect all hoses.
  • It is also recommended to clean the in-line filter.
  • Restore power and run the water heater.

The Rinnai manufacturer provides instructions as described above. This is a safe and effective way of flushing tankless water heaters, which can be done by the owners or a professional plumber.

You can also purchase a flush kit, which generally includes a pump, hoses, hose adapters, a bucket, and descaler as an option. The kits are compatible with tankless valves and can be easily connected.

Manufacturers recommend flushing the mineral deposits from tankless water heaters at least once a year, or more often if you live in an area with hard water.

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