Flushing a Tankless Water Heater

Nov 20, 2023

When it comes to maintaining the efficiency and longevity of your tankless water heater, one essential maintenance task is flushing. Flushing a tankless water heater helps remove mineral buildup and sediment, ensuring optimal performance and preventing potential issues in the future. In this comprehensive guide, we will walk you through the importance of flushing, the step-by-step process, and valuable tips to keep your tankless water heater in perfect condition.

The Importance of Flushing

Over time, minerals and sediment accumulate inside your tankless water heater. These minerals can vary depending on your water source, but common ones include calcium, magnesium, and iron. When they build up inside the heater, it can lead to decreased efficiency, reduced water flow, and potential damage to the unit. Flushing your tankless water heater regularly helps remove these deposits and ensures consistent, hot water flow.

Flushing also prevents clogs and corrosion, which can cause significant damage and reduce the lifespan of your water heater. By flushing your tankless water heater, you not only preserve its performance but also save money in the long run by avoiding costly repairs or premature replacement.

The Step-by-Step Process of Flushing

Before you start flushing your tankless water heater, it is crucial to read and follow the manufacturer's instructions specific to your unit. While the basic process remains the same, there might be slight variations depending on the model. Here is a general overview of how to flush a tankless water heater:

  1. Turn off the power: Begin by disconnecting the power supply to the water heater. This ensures your safety throughout the process.
  2. Turn off the water supply: Locate the main water supply valve and shut it off. This prevents any new water from entering the heater while you're flushing it.
  3. Find the purge port valve: Every tankless water heater has a purge port valve, which is typically located at the bottom of the unit. Consult your user manual to locate it accurately.
  4. Connect a hose: Attach a garden hose to the purge port valve. Ensure the other end of the hose is placed where the water can drain safely, such as a floor drain or outdoor area.
  5. Open hot water faucets: Open one or more hot water faucets in your house. This helps facilitate the flushing process and provides an exit point for the water.
  6. Turn on the purge port valve: Slowly turn on the purge port valve, allowing the water inside the heater to flow out through the hose. Be cautious as the water will likely be hot.
  7. Flush the system: Let the water run through the system for approximately 20-30 minutes, or until the water runs clear without any signs of sediment or mineral buildup.
  8. Turn off the purge port valve: Once the flushing is complete, close the purge port valve to stop the water flow.
  9. Disconnect the hose: Remove the hose from the purge port valve and ensure no water is leaking from any connections.
  10. Turn on the water supply: Turn the main water supply valve back on to restore water flow to the tankless water heater.
  11. Restore power supply: Finally, reconnect the power supply to the water heater to resume its normal operation.

Valuable Tips for Maintaining Your Tankless Water Heater

Regularly flushing your tankless water heater is just one aspect of proper maintenance. Here are some additional tips to help keep your unit in excellent condition:

1. Check the water filter:

Many tankless water heaters have a built-in water filter to catch sediment and impurities. Check and clean the filter regularly to ensure it doesn't become clogged, affecting water flow and efficiency.

2. Schedule professional maintenance:

While regular DIY maintenance is essential, it is recommended to schedule professional maintenance for your tankless water heater at least once a year. Expert technicians can identify potential issues, clean internal components thoroughly, and perform any necessary repairs.

3. Monitor water pressure:

High water pressure can strain your tankless water heater, leading to increased wear and tear. Install a pressure regulator to maintain optimal water pressure and protect your unit.

4. Perform a vinegar flush:

In addition to the regular flushing routine, you can perform a vinegar flush once a year. This helps dissolve stubborn mineral deposits that might not come off during a regular flush. Refer to your user manual for the detailed vinegar flush process.

5. Keep the area around the unit clear:

Ensure the area around your tankless water heater is clear of any clutter, debris, or flammable materials. Proper ventilation is necessary for optimal performance and safety.


Flushing a tankless water heater is a vital maintenance task that should not be overlooked. By flushing your unit regularly, you can prevent issues, ensure consistent hot water flow, and extend the lifespan of your water heater. Remember to consult your specific unit's manual for accurate instructions and reach out to professionals, such as Best Service Plumber, for any expert assistance in water heater installation and repair.