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How to Flush a Tankless Water Heater

Tankless water heater

Tankless water heaters are becoming increasingly popular due to their energy efficiency and endless supply of hot water. However, over time, mineral deposits can build up inside the heater, diminishing its performance and potentially causing damage. Flushing a tankless water heater is a necessary maintenance task to keep it functioning properly. Wondering how to flush a tankless water heater? Start with turning off the power and following the steps to ensure it is done correctly.

Why You Need to Flush a Tankless Water Heater?

Flushing a tankless water heater helps remove mineral deposits that accumulate inside the unit. These deposits can reduce the flow rate of hot water and cause uneven heating. Flushing also helps prolong the lifespan of the heater by preventing corrosion and extending its overall efficiency.

Turn off power to water heater when it is time to flush it.

Steps to Flush a Tankless Water Heater

1. Turn Off the Power

Before beginning the flushing process, make sure to turn off the power supply to the water heater. This can be done by switching off the circuit breaker or unplugging the unit if it is connected to an electrical outlet.

2. Shut Off the Water Supply

Locate the shut-off valves on both the cold water inlet and hot water outlet pipes of the water heater. Close these valves to stop the flow of water into and out of the unit.

3. Connect Hoses

To flush the tankless water heater, you will need to connect hoses to the cold water inlet and hot water outlet valves. Use a pair of pliers to loosen the nuts on these valves and attach the hoses securely.

4. Submerge Hoses in a Bucket of Descaling Solution

Fill a bucket with a recommended descaling solution, such as white vinegar, mixed with water. Ensure the hoses are fully submerged in the solution.

5. Open Valves and Let the Solution Circulate

Open both the cold water inlet and hot water outlet valves to allow the descaling solution to circulate through the tankless water heater. Let the solution run for at least 45 minutes to effectively dissolve the mineral buildup.

6. Rinse With Clean Water

After the recommended time has passed, close the valves and disconnect the hoses from the tankless water heater. Flush the unit thoroughly by running clean water through it to remove any remaining descaling solution.

7. Check for Debris and Signs of Damage

Inspect the internal components of the tankless water heater for any debris or signs of wear and tear. Clear out any accumulated debris and ensure all parts are in good condition.

8. Restore Power and Water Supply

Once everything is clean and in proper order, restore the power supply by turning on the circuit breaker or plugging the unit back in. Open the shut-off valves to allow water to flow into and out of the tankless water heater again.

Tankless water heater that is ready to be flushed.

How Often Should You Flush a Tankless Water Heater?

The frequency of flushing a tankless water heater depends on various factors, including the hardness of the water in your area and the manufacturer’s recommendations. In general, it is recommended to flush the unit at least once a year to maintain optimal performance. However, if you notice a significant decrease in hot water flow or experience issues with the heater, it may be necessary to flush it more frequently.

Other Recommended Maintenance

Now that you know about flushing tankless water heaters, let’s take a look at a few other areas of recommended maintenance.

One of those is knowing the right size of tankless water heater that you need. It will depend on the size of your family and how much water they are using. This is done by calculating the Flow Rate, gallons per minute or (GPM), and temperature pressure.

Another is fixing low water pressure. This is caused by various things such as partially closed valves, debris in pipes, corroded water lines, and leaking water pipes to name a few.

Lastly, if your AC unit is near your water heater and it is leaking water, you may not know which unit is leaking. Take a closer look at the AC unit and it can be leaking because of a clogged drain line, dirty air filter, or low refrigerant.

When Do I Call a Professional?

While flushing a tankless water heater is a task that can be done by homeowners, some individuals may prefer to seek professional assistance. If you are unsure about the process or have concerns about damaging the unit, it is best to hire a licensed plumber or technician who specializes in tankless water heaters.


Flushing a tankless water heater is essential for maintaining its efficiency and prolonging its lifespan. By following the proper steps and doing it regularly, you can ensure that your tankless water heater continues to provide you with an uninterrupted supply of hot water. Honor Services would be happy to come in and complete a full home inspection. Give your local home inspection team a call, Honor Services is your best home Inspection company In Brevard County, FL.

Michelle Shishilla

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