How to Flush a Tankless Water Heater

For the time being, all the water heaters like tankless or traditional tank-type water heaters automatically built upscale deposits, which can reduce the operating power. However, when you decide to buy a new tankless water heater at the same time, you have to think about the maintenance of that tank. Even hard water can contain different minerals, which can cause limescale build-up. The manufacturers recommended that at least once a year, you need to flush your water heater to remove the build-up of lots of minerals at the same time calcium within the unit. Sometimes you need to wash 2 or 3 times a year if the water quality is inferior inside your home.

How to Flush a Tankless Water Heaters


Most units can indicate when you need to flush your water heater. Before cleaning your water heater, you need to know about two things-

  1. Isolation valve
  2. Pumps and flush kits

Isolation valve: The isolation valve allows you to cut off the portion of your pipeline’s liquid or gas supply. It doesn’t shut off the entire amount. There is a wide range of items in your house, from the kitchen to your washroom, with some isolation valves installed for emergency and maintenance purposes. These valves come in various shapes and are classified into two basic types- Like- Rotary movement and linear.

Pumps and flush kits: The submersible pump is best for flushing the tankless water heater. Manual flushing will take lots of time whether a quality submersible pump such as the 91250 from Superior Pump will save hours.

How to Flush The Tankless Water Heater 

Before flushing, the tankless water heater must read the manual properly to get the specific instructions to flush the water heater and descale.

Things we need to use: 

  1. Five-gallon bucket,
  2. Screwdriver
  3. Non-contact electrical tester
  4. Pond pump or small pump
  5. 6- feet long two sections of garden hose with connectors
  6. 5 gallons of white vinegar
  7. Adjustable wrench
  8. Needle nose pliers
  9. Submersible pump

Generally, the gas tankless water heater flushing system and the electric tankless water heater flushing system are different. Two different types of techniques we should follow during flushing these two types of water heaters-

Flushing system of the gas tankless water heater

All kinds of gas tankless water heaters have the same flushing system. Now, I am trying to discuss details step by step here-

Step-1: Preparation

  • Disconnect the electrical power.
  • Disconnect the access panel and use a non-contact electrical tester to check that no power passes to the terminal.
  • Identify and close the gas isolation valve.
  • Identify the hot and cold shut-off valves and close those to prevent the unit. from getting any water inside the unit
  • Identify and locate the hot water pressure relief valve from the hot water line, open the lid to release the pressure, and be careful because the water is boiling.
  • Now, connect the hoses to both hot and cold water service ports.
  • At that time, you fixed your submersible pump with a 5-gallon bucket.
  • Now, fixed the cold water hose with the pump.
  • After that, you have to fix the free end of the hot water hose with the bucket.
  • Last, of all, pour 5 gallons of regular quality white vinegar into the bucket.

Step- 2: Flushing:

  • First of all, open the hot and cold service ports and turn the pump on.
  • Let the vinegar circulate through the heater for at least one hour. This process can break down the scale and flush out the sediment inside the unit.
  • After that, turn the pump off and dump the vinegar.
  • Now, remove the attached hose after closing down the service port.
  • At that time, open the cold water shut-off valve and flush out any remaining vinegar through the second hose into the bucket for near about ten minutes.
  • Now close the cold water shut-off valve.
  • Remove the 2nd hose after letting the water finish draining.
  • Now close the hot water service port.
  • If there are a cold water inlet filter and hot water in-line filter inside the tank, remove it.
  • Last, of all, flush the filter at a sink to remove any sediment residue.

Step-3: Clean up:

  • Be careful when replacing the filter and opening the hot and cold water shut-off valves.
  • Now, you have to replace the access panel.
  • At that time, open the gas shut-off valve.
  • And finally, reconnect all the electric supplies properly.

Flushing system of the electric tankless water heater

There is a bit of difference between the flushing system of a gas water heater and an electric water heater. We need some additional steps to maintain the flushing system accurately.

Similarly, the electric tankless water heater flushing system has three steps. Like-

Step-1: Preparation:

  • Close all the electrical supplies at the breaker.
  • Disconnect the cold water shut-off valve.
  • Now open your faucet to drain the left water from the heater.
  • Disconnect the hot water shut-off valve.
  • Disconnect the access panel and test whether there is an electric connection with the heater with a non-contact voltage tester.
  • Remove all the screw connections with the heating elements.
  • Now, lose the hexagonal brass top of the heating element in a counterclockwise direction, which is very helpful to remove the heating elements.
  • Any cracked element needs to be replaced and checked all the heating elements.
  • We need to finally store all the heating elements inside the Cooper chamber for cleaning.

Step-2: Flushing:

  • Fill the Cooper chambers with virgin white vinegar.
  • Let the vinegar sit in the chamber for 90 min to 2 hours. Now drain the vinegar. This process will break all the scales on those elements.
  • Change the heating elements and then check all the wires.
  • Now the time is to open the cold water shut-off valve and then fill the tank.
  • Do the paper towel test to check the tank for any signs of leaks.
  • Now, this is the perfect time to open the hot water shut–off valve.
  • Finally, open more than one hot water faucet and give near about five minutes to pass the water to flush out the vinegar and other materials inside the line.

Step-3: Cleanup:

  • Turn off all the hot water taps inside the tank.
  • Reconnect the power system and close all the access panels of the electric tankless water heater. Then, close the cold water shut-off valve.
  • Now, it’s time to remove the cold water inlet filter and flush it to clean any particles.
  • Be careful; It’s time to replace the filter carefully.

So, this is the whole flushing procedure you have to perform during flushing your tankless water heater, whether it is gas-powered or electric. You cannot leave any step during flushing your tool. Hopefully, you can do all the processes accurately and enjoy the service of your tankless water heater for a long time.

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