How To Flush A Tankless Water Heater – Flushing Gas And Electrical Units

Tankless Water Heaters are effective and highly productive but to maintain efficiency their flushing is compulsory. That is why we have explained how to flush a tankless water heater in this article with some tricks and tips.

For most of the water types, flushing will be enough to do annually but in the case of hard water, this process should be repeated often.

Why Is It Necessary To Flush A Tankless Water Heater?


Over time, calcium and other debris start to gather in the filter of the tankless water heater. There is a risk of explosion in the tank if these limescale deposits are not removed.

While there is no such explosion in tankless water heaters, the efficiency of the machine will be reduced. So, it’s important to flush a tankless water heater to avoid any kind of problem compromising the life span of the machine.

How Often Do You Need To Flush A Tankless Water Heater?

You might be using a tankless water heater for a long time and there must have a question popping in your head about how often you need to flush your tankless water heater. It is highly recommended by the manufacturers of heaters to flush it annually.

If you live in an area where there is plenty of hard water, you need to flush it more often. Hard water contains lots of elements like calcium, lime deposits, or other elemental debris so they need to be removed as fast as you can.

Preparation to Flush

For starting the preparation of flushing, all you have to get few gallons of vinegar might be 4 or 5. You don’t need to spend lots of money on it as it is an extremely cheap process.

Necessary things

There is the requirement of some supplies that will help you during the whole process. These supplies are mostly recommended by manufacturers.

  • Screw Driver
  • Vinegar
  • Pliers with needle nose
  • Wrench
  • Hoses (2)
  • Voltage Tester
  • Submersible Pump

Isolation Valves


Before starting the initial steps of the process, it is important to isolate valves. An isolation valve will cut off the gas or liquid supply, which means isolating a portion of the pipeline without shutting off the entire power supply.

Sometimes manufacturers do not install the feature of an isolation valve into your heater but it can challenge the safety measures to a great extent. So, it is better to do its installation by hiring a technician before flushing your tankless water heater.

Pumps And Flush Kits Usage

A submersible pump will be required to flush a tankless water heater. In a tank heater, you have a large amount of water to sweep up debris and sediments but in the tankless water heater, you need to have a pump to save hours of flushing.

A flush kit includes a bucket, hoses, pump, and descaler. These tools are important to flush a tankless water heater.

How To Flush A Gas Tankless Water Heater?

For a gas tankless water heater first, you should check the manual for the instruction to flush your water heater. These manuals should be used as guidelines for the whole procedure.


  • Disconnect all the electrical connections to the water heater.
  • Use a voltage tester to test the wires going into the terminal to ensure no electric supply reaches the unit.
  • To stop the passage of cold water into the unit or system, shut off hot and cold water valves.
  • To relieve pressure, open up the hot water pressure relief valve.
  • One end of Hose 1 should be connected to cold water and the other ends to the submersible pump and place the pump into a bucket (5 gallons)
  • One end of Hose 2 should be connected to hot water while another end into the bucket.
  • Add 4 gallons of vinegar into 5 gallons of bucket
  • Circulate vinegar through the unit for at least 60 minutes by turning on a submersible pump. The rate at which the pump circulates should be 4 gallons per minute but if the pump is circulating at a slower rate, then vinegar should circulate for a long time.
  • The submersible pump should be turned off and dispose of vinegar


  • Now remove the unconnected end of Hose 2 from the bucket and place it outside
  • Also, remove Hose 1, turn off the cold water service port, and open the cold water shut-off valve.
  • Freshwater will start to flush out leftover vinegar through Hose 2 when the cold water service valve will be opened.
  • Run water for at least 10 minutes and close the cold water shut-off valve.
  • When water evacuates, detach Hose 2 and close the hot water service port.

Cleanup Inlet Filter:

  • First remove the cold water inlet filter, if you have that one because some manufacturers use a hot water inlet filter.
  • Use tap water to flush the cold water through the inlet filter
  • Turn on cold water shut-off valve by replacing cold water inlet filter
  • Open hot water vale
  • Turn on all electrical connections of the unit and remove the panel cover

How To Flush An Electric Tankless Water Heater?

To flush an electric tankless water heater, you can either take help from the manual or hire a professional. Here we’re presenting every minor detail of the whole procedure, so you can do it on your own.


  • Turn off electrical connections at the circuit breaker
  • To prevent water from flowing into the unit, close the cold water shut-off valve.
  • To evacuate water from the unit open a faucet
  • Close hot water shut off valve
  • Use a voltage tester to find out there is no passage of electricity

Detach Heating Elements:

  • Detach wires by unscrewing the screws
  • Remove heating elements by rotating hexagon brass counterclockwise
  • Check out if there is any crack, if you find them replaced them immediately
  • Implant heating elements in the copper chamber
  • Fill this chamber with vinegar and leave it for 120 minutes
  • Replace heating elements and evacuate vinegar from it

Clean off Vinegar:

  • Open cold water shut-off valve and fill the tank with water
  • Carefully check for leaks
  • Now open hot water shut off valve
  • Turn on all hot water taps to run water for at least 5 minutes through faucets. It will flush out the vinegar and remove air pockets in the pipe.

Cleanup Inlet Filter:

  • Detach cold water inlet filter on the line of cold water leading inside the tank
  • Flush all the debris and sediments
  • Place the filter back on the cold water line


  • Never flush the tankless water heater without turning off all the electrical connections
  • If you forget to turn off the electrical supply then it will cause huge damage to the unit
  • There should be at least more than one source of power.
  • Make sure to flush a tankless water heater once a year
  • Never ignore the exterior maintenance to cleanse off the rust and check out cracks or splits so no chance of leakage could occur.
  • Test the pressure relief valve, if you don’t have it go for its installation.
About Zarmish Fakhar

Zarmish has been working as a freelance research writer for 5 years. She is a Zoologist and social media activist as well. She has worked for many reputable newspapers including Dawn. She is a valuable member of Aqua macho as her passion for clean water and eco-friendly products are booming day by day.

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