How to Clean a Tankless Water Heater [A Complete Guide]

cleaning tankless water heater

Tankless water heaters tend to require less maintenance than storage systems, but they do need regular cleaning.

There is no set time frame for maintenance, as it is dependent on the hardness of the water. Systems in areas of hard water will require cleaning more often than those in soft water areas because the mineral deposits build up quicker.

This generally takes longer in a tankless system because it pushes the minerals through the system, rather than allowing a build up at the bottom of a tank. Most tankless water heaters will have an alert when they require maintenance.

How to Clean a Tankless Water Heater

How to Clean a Tankless Water Heater# Step One: Shut off the power supply. If the tankless water heater is gas, then shut off the gas supply. If it is electric, turn off the circuit breaker. Gather all the supplies that will be needed.

You will need:

  • Five-gallon bucket
  • Two stainless steel washing machine hoses
  • A submersible pump
  • Four gallons of white vinegar, (food grade)

If you don’t have these items, they can be purchased in a kit.

# Step Two: Shut off the three water valves. One is for cold water into the system and is usually blue, one is for hot water out of the system and is usually red, and one is for the water supply to the home and maybe yellow. These can be handles or knobs, depending on the make and model of your tankless water heater.

If they are handles then when they are in line with the pipe, the water is turned on. When they are perpendicular to the pipe, the water is turned off. If you haven’t done so, unplug the unit from the wall socket.

# Step Three: Take off the purge port valve caps from the purge valves on the hot and cold water. They have small handles this needs to be done slowly to relieve any build up of pressure and to avoid any hot water spillage. The caps need to be handled with care to make sure the rubber washer sealing discs remain in place.

# Step Four: Attach the housing lines to the valves to direct the water into the bucket. Take extra care when attaching the hose to the hot water. Open the purge ports to allow the water to flow into the bucket. The hot water side will drain much faster and with more water than the cold water side, so you should open the hot side slowly and let it trickle out first to test the temperature, before opening it fully.

# Step Five: When the water has finished draining, leave the hoses in place, and empty the bucket. Fill the bucket with four gallons of food grade white vinegar. Vinegar is a good non-chemical cleaning solution. You shouldn’t use chemicals or other vinegar for cleaning the water system as they can affect your health and the health of the water system.

Once you have filled the bucket with vinegar, attach the end of the hoses to the submersible pump and place it into the vinegar before plugging it in or turning it on. When you turn it on, it will start to pump the vinegar through the system. Leave it to run for around forty-five to ninety minutes.

# Step Six: While the pump is pumping the vinegar, remove the face plate of the heater, and remove the air filter. Rinse it and dry it off, and replace it. Screw the faceplate back into place.

# Step Seven: When the vinegar has finished pumping, unplug the pump, and remove it from the bucket of vinegar. Empty the vinegar and place the bucket under the water heater. Remove the hose from the cold water side and screw the cap back in place. Open the water valve and let 4 to 5 gallons of water flow through the system. Close the valve. Unscrew the water filters and rinse them before putting them back into place.

# Step Eight: Attach the caps and put everything back in place. Once everything is securely capped, turn on the cold water valve, and listen for water. Then turn on the hot water, and finally the gas and central circulation valve. Then you can plug the system back in and run as normal.


These steps may vary slightly from brand to brand or model to model. Read the manufacturer’s booklet for your specific make and model. Some models include hoses for cleaning, others might not. If you need to, you can buy a tankless water heater cleaning kit.

You can buy food grade white vinegar in bulk online or in certain stores. Never use any other kind of vinegar as it can damage or stain the system, and you shouldn’t use chemicals as they can remain in the water and harm your health.


Never clean your tankless water heater without turning off the power and the gas. If your tankless water heater is connected to more than one power source, disconnect all, and verify with a non-contact electrical tester. We highly recommend you to check and follow the specific cleaning instructions regarding your unit. Any mishandling can lead to damage that may require service/repair.

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