How to Descale a Tankless Water Heater

Tankless water heaters have become a popular energy-efficient alternative to the standard tank-style water heaters we know so well. Aside from their increased energy-efficiency and eco-friendly operation, tankless water heaters have much to offer home and business owners alike. One of the most important responsibilities of owning a tankless water heater is regular maintenance. This includes annual inspections and service from a licensed plumbing contractor, as well as, routine descaling. Although it is recommended to call a licensed plumber for water heater descaling services, it is a job any handy homeowner can accomplish themselves.

Water Heater Repair and Service 317-784-1870

Water Heater Repair and Service 317-784-1870

Descaling a Tankless Hot Water Heater

In areas with hard water, lime and scale can build up on the inside walls of the heat exchanger, causing problems for the entire unit. It is recommended to have your tankless water heater descaled once per year. You can choose to appoint the duty to a local and licensed plumber, or, you can choose to undertake the task yourself. If you wish to move forward on your own, be sure to review the basic steps of descaling a tankless hot water heater first. Look below to get started doing just that!

Tip: If your tankless water heater does not come equipped with isolation valves, you need to call a contractor for professional service!

What You’ll Need:

✔ 5-Gallon Bucket
✔ 3 Gallons Virgin White Vinegar
✔ Submersible Circulation Pump (available at any home improvement store)
✔ Two Small Garden Hoses


1. Turn off all power (gas or electricity) the water heater. Switch the breaker in the electrical box or shut off the main gas.

2. Shut off all water supply to the entire property, including the hot and cold water heater valves. No water should be coming into the house or into the water heater. These handles usually turn north to south and are located on the side of the hot and cold valves.

3. Be sure the hot and cold water valves are also closed. These are generally labeled red and blue and turn side to side.

4. Carefully remove the purge port valve caps. Place them somewhere gently so the rubber washer discs do not dislodge and they are not lost. You may feel some pressure when doing this, but just make sure the hot water valve is closed and you should be safe.

5. Fill the bucket with 3 gallons of white vinegar. Be sure the bucket is in a stable position and it won’t tip over once full.

6. Connect the hot and cold water hoses to the correct valves.

7. Connect the other end of the cold water hose to the output of the circulation pump.

8. Place the pump inside the bucket of vinegar.

9. Place the other end of the hot water hose inside the bucket.

10. Open the cold and hot water valves back up by turning them half-way, so the levers are parallel to the hoses. This will allow vinegar to flow up from the bucket, through the pump, up to the water heater, then back out of the hot water valve, and then back into the bucket. This flushes all the solid deposits from inside the tank.

11. To get that started, plug in your circulation pump and turn it on.

12. To be sure water is flushing properly, slowly lift the outlet hose out of the vinegar and check that water is coming out.

13. Allow the system to circulate for one hour, no longer.

14. When finished, turn off the pump and drain the vinegar from the tank.

15. Close the cold water valve.

16. Open the main cold water supply valve and flush cold clean water through the tank for 5 minutes to clear out any residual vinegar. Then close the main water valve.

17. Remove the filter screen from the inlet of the cold water valve and clear any buildup. Replace it when finished.

18. Disconnect the hoses, and replace purge caps.

19. Close the hot and cold water valves.

20. Open the main cold and hot water supply valves.

21. Turn the power back on.

22. Run hot water from a few faucets around the house and check for any performance issues.

Indianapolis Water Heater Service

Weilhammer Plumbing Company 317-784-1870

Weilhammer Plumbing Company 317-784-1870

Call Weilhammer Plumbing Company at 317-784-1870 for tankless water heater service in Indianapolis, Indiana. Owner, Mark Weilhammer, and his team of licensed plumbers, service all make and model water heaters for both residential and commercial properties. We provide water heater repair, service, installation, and replacement at the most competitive prices in town. Call 317-784-1870 for Indianapolis water heater service, today.