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Maintenance Tips for Your Tankless Water Heater

Protect your investment in a tankless water heater by maintaining it correctly. You need a little equipment, some patience, and a thorough understanding of your system. These tips apply to most brands, but every system is different, so check your unit’s manual for specifics.

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Should You Even Do It?

If you have any doubts about your ability to perform a maintenance task, don’t do it! Call a professional and tell them you’d like guidance from the service technician. If you are clear about your needs when you schedule the call, they know to allow a little extra time to explain proper maintenance.

How Often?

If you have untreated hard water, clean the system every six months. If you have a city water supply, once a year may be enough, but follow manufacturer’s recommendations.

Safety First!

Safely turning everything off takes about five minutes. Always turn off the power and (if applicable) gas to the unit. Next, turn off the water supply. Your unit should have cutoff valves on both hot and cold sides. It should also have isolation valves, allowing you to de-scale the system.

  • The gas shutoff valve will be a T-valve: if the handle lines up with the gas line, gas is still flowing. If the handle is perpendicular to the line, the gas is off.
  • Turn the shutoff valves for hot and cold water.
  • The hot water isolation valve out from your heater will probably be a red handle. Turn it 90º to prevent hot water from leaving the unit when you hook up hoses for descaling.
  • The cold water isolation valve may be a blue handle. Turn it 90º to allow you to hook up the feeder hose for descaling.
  • Really hot water may be present in small amounts in the pipes within your tankless water heater. Be careful!

Reassess Your Needs

As your family grows so will your need for hot water. You may want to consider adding additional units. If your tankless water heater in the basement or on an outside wall is answering calls for hot water throughout your house, you are wasting water and energy. A second unit installed near the washing machine or in a newly renovated bathroom will save money and aggravation.


Water going into your tankless water heater may have grit or other minerals in it. For your system to work efficiently, the cold water supply needs to be clean and at full pressure. Cleaning the filter takes about ten minutes. Look just below the cold water inlet to find the filter.

  • Usually the filter is at a right angle to the cold water inlet, often with a black cap.
  • Turn the filter to unscrew it and gently slide it out. It should be hand-tight, so you should not need a wrench.
  • The filter may look like a wire mesh cylinder. If it is clear—no grit or chips—you’re in good shape. Just screw it back in.
  • If it has debris, clean it. Run under water to wash away any grit or other contaminants.
  • Replace the filter.


Lime scale builds up in the heating elements in a tankless water heater. You can use household vinegar to rid of this quickly and safely. De-scaling requires about an hour, a small submersible pump, two hose lines, and plenty of vinegar. Two to four gallons is recommended by most manufacturers.

  • If you’ve turned off isolation valves for hot and cold water sides, you can remove the valve caps that are protecting the threads at the connection for your cold water and hot water hoses.
  • Connect a six-foot hose to your cold water side, and another six-foot hose to the hot water side. This is to pump vinegar in through the cold side and out from the hot side.
  • Attach the cold water hose to your pump.
  • Place the bucket on a stool or stable chair close to your tankless water heater.
  • Place the pump into a five-gallon bucket. Plug the pump in and pour two to four gallons of vinegar into the bucket.
  • Run the hot water side hose into the bottom of the bucket.
  • Start the pump and check to make sure you have flow in and out. Allow the vinegar to circulate for 20 to 50 minutes.
  • After de-scaling rinse out the system for around 20 minutes by replacing the vinegar with cold water.
  • Turn off the pump, allow the rinse water to drain out the hot water side completely, turn the isolation valves, and disconnect the hoses.
  • Replace the valve caps, turn the cutoff valves on, and turn the gas and power back on.