How To Flush Your Tankless Water Heater

Learn how to flush your home's tankless water heater with a few basic tools in about an hour. This should be done at least once a year.

If you own a tankless water heater, it is highly recommended that you flush your water heater at least once per year to prevent the buildup of calcium and other minerals. If it is not consistently flushed, corrosion can occur and greatly decrease the longevity of your water heater and reduces your need of a water heater repair service. Luckily, you don’t need a tankless water heater flush kit – you can do this with household items! This process usually takes at least one hour, if you have all your materials prepped.

Required Tools:

Step 1: Isolate Re-Circulation Pump

Identify every isolation valve in the plumbing line for the re-circulation pump. Each valve should be a ball valve (meaning there is a ball inside the piping used to seal the flow), with a long thin handle, covered with a light colored rubber grip. Turning these a quarter turn (90 degrees) in either direction will stop the flow of water.

Step 2: Shut Off Blue (Cold) Water Valve on Bypass Line of Water Heater

A quarter turn in either direction will turn off the flow of water. If it is difficult to turn, you may need a wrench to make it easier.

Step 3: Shut Off Red (Hot) Water Valve on Bypass Line of Water Heater

A quarter turn in either direction will turn off the flow of water. If it is difficult to turn, you may need a wrench to make it easier.

Step 4: Turn Off Water Heater

This is usually located near the LCD screen which shows the temperature of your water. For gas water heaters, there may be a gas valve to cut flow of gas to the heater instead.

Step 5: Turn Off Re-Circulation Pump

Find the pump control, which looks like a timer with a dial. There should be a plastic cover on it, so if there is, remove it. Then flip the on/off switch to the off position. Put the cover back on so you don’t lose it.

Step 6: Turn Off the Temperature & Pressure Release Valve

This valve should look like a metal switch without a colored identifier like the other valves, and if flipped, points outward away from the piping. Flip that switch now.

Step 7: Locate, Remove & Clean the Inline Filter Screen

This should be located directly under the water heater, and usually has a black plastic cap with ridges, allowing you to grip it with your hand or a wrench. Unscrew it, remove it and clean out any gunk from within the tube and screen.

After cleaning it out, put it back in and tighten it. Note: This seals with an O-Ring, so don’t over tighten, or it may leak or crack.

Step 8: Empty Vinegar into 5 Gallon Bucket

Empty the entire gallon of white vinegar into the bucket, then add water so the bucket is filled half way, effectively diluting the vinegar.

Step 9: Hook Up Washing Machine Hoses to Lines

There are two bypass lines, one hot and one cold. They have red and blue valves and a piping line with a plastic or rubber cap at the end. You will need to remove those caps and proceed.

Use the first hose to hook up the hot side return from the water heater, while the other end goes into the bucket.

Then, use the other hose to hook up the cold water feed from the water heater and have the other side go into the outlet of the water pump.

Step 10: Turn On Bypass Line Valves

These bypass lines allow for you to cut flow to and from external sources, so you can work directly with the water heater locally. By turning on the valves, the water will be redirected to their respective inlet/outlet.

Step 11: Hook Pump to Suction Strainer

Hook the clear hose included with the pump, from the inlet of the pump to the suction strainer (the triangular piece), which you will place inside the bucket of vinegar-water.

Step 12: Plug the Pump into a Wall Outlet

Now, the pump should activate (unless it has a power switch, in which case, turn it on now). Double check anywhere for leaks in case of insecurely tightened connections. Then let the pump do all the work. The process should take about 30 minutes.

Step 13: Dump Bucket Out, Replace With Fresh Water

Let this fresh, clean water circulate for 15 minutes.

Step 14: Turn Bypass Valves Back Off

It’s best to do this before unhooking the hoses, unless you desire some splash.

Step 15: Turn On Pressure Release Valve, Disconnect your Hoses

Disconnect both hoses and replace the cap on the line.

Step 16: Turn Hot and Cold Lines Back On

This should allow flow to and from external sources again.

Step 17: Remove Air Pockets from Water Heater

To do this, you will need to connect a hose back up to the hot water bypass return line. This will help remove any air pockets from the system and cause it to drain out any remaining water. Use a long hose if you intend to drain outside, or a short one if you want to drain into your bucket. Flip the valve on the return line again to let it drain out.

Step 18: Final Steps

To finalize the entire process you can now, in this order:

And there you have it! You’ve successfully flushed your water heater on your own. Clean up and properly store your tools so that they are available for your next needed water heater flushing.

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If you need help with this process, have a plumbing emergency, or other plumbing problems that needs professional service, Pure Plumbing is available 24/7. Call us at (702) 710-7388 to get help immediately or to schedule an appointment with a qualified Las Vegas plumber. We are here to help!

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