How To Drain & Flush a Tankless Water Heater

Tankless water heaters typically need flushing at least once every year. Possible every 6 months, depending on the hardness of your local water and the amount of usage of your water heater. Regular tankless water heater flushing will help prevent potentially damaging large buildup of sediments, such as limescale.

Tankless water heaters have increasingly become a popular heating choice. They are cheaper and more efficient to run. Tankless models only require less space and heat water when needed.

Just like traditional water heaters, tankless models will also be exposed to sediment buildup and harsh minerals. A tankless water heater needs to be flushed at least once a year to ensure the unit has optimal performance and efficiency.

Follow this simple process on how to flush a tankless water heater.

Step by Step Guide

Tools You Will Need

To flush your tankless water heater, you’ll need:

  1. Two 2 metre length garden hoses
  2. A sump pump
  3. A 5-gallon bucket filled with approximately 3 gallons of white vinegar

The procedure for flushing a tankless water heater is slightly different from flushing a traditional water heater. Here’s what you need to do.

Turn off the power supply to the water heater. If your water heater uses gas, turn off the gas at the gas shutoff valve.

Turn off the inlet and outlet water shutoff valves to the pipes that feed water into and out of your water heater.

Your tankless water heater should have 2 threaded drain valves. If it doesn’t, you’ll need to have a plumber install these to allow you to periodically flush your water heater to keep it clean and well maintained.

Attach one end of one of your garden hoses to the outlet of the sump pump and place it into the bucket of white vinegar. Screw the opposite end of the garden hose into the water inlet isolation valve that leads into the water tank.

With the second 2-meter length garden hose, connect one end to the hot water outlet isolation valve and the other end into the bucket of white vinegar. This will allow you to pump vinegar into the water tank, then out again through the outlet isolation valve and back into the bucket.

Next, open the hot and cold isolation valves on the water heater and turn on the sump pump to circulate vinegar through the heater.

Allow the vinegar to flush through the tank for approximately 60 to 90 minutes.

Once you have thoroughly flushed the water tank with vinegar, stop the pump and dispose of the vinegar.

Place the open-ended hose back into the bucket, open up the cold water shutoff valve, and allow the mains water to flow into the bucket for approximately 5 minutes to flush out any remaining vinegar. Close the cold water inlet shutoff valve.

Once that’s done, shut off the isolation valves, remove the hoses and then first open up the water outlet shutoff valve, then the cold water inlet shutoff valve.

You can now turn the gas and electricity back on. Open up a couple of faucets in the home to bleed any air out of the pipework.

Your tankless water should now be thoroughly clean and ready for use for another 6 to 12 months.

Always check the user manual, as it may have specific instructions to flush and descale a tankless water heater. If you don’t feel confident flushing a tankless water heater yourself, call a plumbing repair to get the job done.

Leave a Comment