How to Maintain Your Tankless Hot Water Heater in 9 Simple Steps

A tankless water heater can feel like a miracle for your home. When used within its limits, you can receive an unlimited supply of hot water, at your preferred temperature, without the need for a storage tank.

The best tankless water heaters are even energy efficient today. Just look for the Energy Star label on the unit that you prefer.

Like any appliance for the home, there are some maintenance requirements that a tankless water heater requires to continue operating as it should. When you can keep your water heater operating at peak efficiency, it will be able to provide you with 20+ years of service.

Here are the steps you’ll want to take to ensure you are safely and effectively maintaining your tankless water heater.

Step 1: Turn off the power

Never work on your tankless water heater while it is connected to a power source. You can turn the power off to the unit by flipping the breaker to which it is wired. If you are using a gas-powered tankless water heater, then you’ll need to shut off the gas to it. There should be a lever that allows you to turn off the gas to the unit. Some models may require you to turn off the main gas value.

Note: If you turn off the main gas valve to your home, you will need to ignite the pilot lights to all your appliances once again.

Step 2: Turn off the water valves

In the standard setup, a tankless water heater utilizes three water valves. You’ll need to close, or turn off, all 3 valves that are associated with the unit.

If you have a non-traditional setup for your water heater, then turn off all the valves that are associated with the unit.

You must turn off the valves because this will prevent cold water from going into the water heater. It will also prevent hot water from entering the plumbing system in your home.

Cold water valves are generally designated with a blue color. Hot water valves are designated in red. If they are not color-coded, then look for the words “cold” or “hot” on the valve itself.

The third valve is the primary valve that brings water into your home. You’ll want to turn that off as well.

Step 3: Remove the purge port valve caps

Look for the purge valves with your setup. They will have a lever that resembles the letter “T” and will be located near the valves. You’ll need to close these valves completely because it will relieve whatever water pressure is remaining within the water heater.

The last thing you want is to have high-pressure hot water blasting out toward your face.

Once you have closed the valves, give the system a minute or two to relieve some of the pressure. Then slowly remove the valve caps that are located on the end of your cold water and hot water valves.

Note: You need these caps to stay in place and stay clean. Without them, your water heater will not operate properly. Allow them to hang loosely from the valve. If this is not possible, set them aside in a clean, dry location.

Step 4: Attach your hosing lines 

Most tankless water heaters come with hosing lines that will be used to clean the system. The lines must be long enough to reach a bucket that is away from your unit.

You will need to purchase these lines if your unit did not come with them. Consult your owner’s manual to ensure you purchase compatible hosing lines. 

There will be exact instructions to follow during this step from your unit’s manufacturer. These must be followed. You may be required to use a sump pump to complete the process.

Step 5: Open the purge port valves

Once you have connected your hosing and have the lines placed in a bucket, near a drain, or some other safe discharge location, then you’re ready to open your purge port valves. They should return to a perpendicular position.

Step 6: Clean your tankless water heater

Once the lines have been fully purged, you’re ready to clean out your tankless water heater. Most water contains scale on some level. These minerals may be helpful to the human body, but they are not helpful to the functionality of the water heater itself. Over time, scale can build up significantly, impairing water flow through the unit.

Untreated scale can even damage some tankless water heaters.

Chemical cleaning solutions should never be used in a tankless water heater to clean it. Chemical cleaners may leave residues that could be harmful to the health of your family. Only use natural products to clean it.

The best option is to use an undiluted white vinegar. Most tankless water heaters can be thoroughly cleaned with 3 gallons of vinegar or less.

You will need to follow the draining and flushing procedures that are recommended by the manufacturer of your water heater.

Some tankless water heaters may require 45-60 minutes of flushing to properly clean the unit.

Step 7: Close the purge port valves again

Once the cleaning procedure has been completed, you’ll need to close the purge port valves once again. Twist the valves back into a parallel position to ensure that they have been fully closed.

Give the system a minute or two to allow any pressure which may remain within the unit to escape. Then you’ll be able to disconnect your hosing lines from the water valves. Be sure that all hosing lines are fully removed.

Then you can replace the purge port valve caps back into place. You’ll need to tighten the caps to a finger-tight connection to ensure that you do not receive any leaks.

Note: Keep in mind that the purge port valve caps are usually just sealing discs that are made of rubber. If you tighten them with too much torque, there is a good chance that you will damage the rubber.

Step 8: Restart your tankless water heater

Each water heater will have specific restart instructions that must be followed. Consult with your owner’s manual to ensure all the steps are followed in their exact order. Be prepared to flip the breakers back on for your unit or to restore gas to the water heater.

Some jurisdictions may require a professional technician from the local gas utility to supervise the restoration of gas to your tankless water heater.

Some tankless water heaters may require you to open, or rotate, the cold and hot water valves to be in a parallel position to the main water valve that leads into the home.

Step 9: Get the air out of your system

No matter how carefully you’ve followed these steps, there will be air that gets trapped within your home’s plumbing system. You’ll want to slowly turn on a hot water tap at your furthest faucet away from the water heater to purge the air from the system.

It will take 2-3 minutes of the water running through the tap to purge the air from the entire system. Some larger homes, usually 2,500 square feet in size or larger, may require multiple faucets to be running to completely purge the air from the system.

If there is a large amount of air that is being pushed through the system, you may see the water flow be reduced or completely stop as the air escapes. Depending upon the amount of pressure that is created by this process, there may be some loud thumping sounds or vibration at the faucet. This is normal.

Large amounts of air trapped in a plumbing system can cause damage if it is allowed to escape too quickly. Open your faucets slowly and only partially to avoid this situation if you are concerned about it.

How Often Does a Tankless Water Heater Need to Be Cleaned?

There are no set rules which apply to the maintenance schedule of a tankless water heater. Many homeowners will clean out their units once per year and find that to be a suitable schedule. Some manufacturers may have specific recommendations that must be considered as well.

To determine how often the water heater should be cleaned, an evaluation of water hardness must occur. If water is very hard, then the scale will build up quickly within the unit and servicing might be required every 6 months.

If you have softer water, or if your tankless water heater is hooked up to your home’s plumbing system after a water softener, then you may only need to clean it once every 3-4 years.

Some water heaters come equipped with a scale detection system. If your system has this technology, then you’ll want to clean it when the system indicates that it is required.

If you take care of your tankless water heater, it will take care of you. Follow these steps and you’ll have a successful experience.

Looking to purchase a new water heater or replace an old one? Check out our reviews and buying guide post.

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  1. Mike Pius

    May 20, 2019 at 1:40 pm

    Thanks for the heads up. A lot of people need this to help maintain there water heaters. These devices are quite expensive and one cant afford it developing fault due to a simple mistake you can avoid.


  2. richard

    November 10, 2019 at 8:56 am

    my propane ,battery ignition Tankless water heater doesn’t spark after standing for a few years unused. It makes a click but there is no gas flowing or ignition spark . the old batteries were corroded and replaced .the battery compartment and terminals were cleaned . there is a good flow of water .and a new tank of gas.


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Greg Mattson

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