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How to flush your tankless water heater

Posted on: April 10, 2012

As you may already know, a properly maintained tankless water heater should last you as many as 25 years or more. But what’s involved with “proper tankless water heater maintenance”?

The Problem with Hard Water

The number one enemy of tankless water heaters everywhere is hard water scale that builds up primarily on heat exchangers. Over time, the buildup can cause the heat exchanger to overheat, which will then cause it to send an error code to lock out the system. Many times, this can totally cut off your access to hot water until you get the problem fixed!

The best way to avoid hard scale buildup in your tankless water heater is take a few easy preventative maintenance steps:

  • Install a whole house water softener in your home to decrease the level of scale buildup not just in your tankless water heater, but in your dishwasher, washing machine, sinks, etc. A water softener will also help your water taste better and wash off soap better.
  • Flush your tankless water heater periodically – every 6 months to a year. This is not too difficult and many people find it easier to do themselves.

How to Flush a Tankless Water Heater

To start, you’ll need a small sump pump (1/6HP will work fine), two small hoses, two to three gallons of white vinegar and one gallon of water.

  • Remove the cover plate and expose the ignition source (either gas or electric) as well as the shut off valves and water connections (check your owner’s manual for specific details on how to do this).
  • Shut off all lines as well as the water inlet and outlet sources. If your system has more than one source of power, be sure to turn both off.
  • Release the water pressure by opening the overflow valve (again, check the manual for details).
  • Connect one end of one of the hoses to the OUTPUT connection on the water heater. Connect the other end of the same hose to the INPUT connection. Connect one end of the other hose to the OUTPUT connection, and leave the other end of that hose in the bucket.
  • Place the sump pump in the bucket and add the vinegar and water to it. Make sure the pump is submerged in the mixture and the hose connected to the OUTPUT connection is running into the bucket.
  • Start the pump and allow the vinegar to cycle for 45 minutes. This process will remove the lime and calcium, clearing out the system and allowing your Gaithersburg tankless water heater to run like new!