How To Descale A Tankless Water Heater

Protect Your Investment—And Your Comfort!

water heater repair tennesseeWhen you have a conventional water heater with a tank, you have to maintain it by periodically checking the anode rod and draining the tank to prevent sediment buildup and tank corrosion, among other things.

But with a tankless water heater, no tank means no work, right?


While there is no tank that can fail, there are other issues that can impact your tankless water heater’s operation and its efficiency.

One big problem is the buildup of limescale on the heat exchanger of your tankless water heater. It also happens in conventional tank water heaters. But with your tankless water heater, even a thin layer of limescale can reduce its efficiency by 30%. That pretty much negates any efficiency advantage a tankless water heater has over conventional storage water heaters with a tank.

Dealing with this problem may sound scary, but it isn’t. This is a relatively straightforward DIY project that you can do to help keep your propane tankless water heater running efficiently. This should be done at least once a year.

By the way, your tankless water heater should have professional maintenance as well at least once every two years as well!

Descaling 101

The first step in any work on propane appliances is, read the owner’s manual. Instructions may vary slightly between models, so make sure you thoroughly read them, so you know exactly what to do.

Once you’re done with that, gather your materials:

  • A tankless water heater flush pump
  • Rubber or washing machine hoses
  • A bucket to collect water
  • Tankless water heater descaling solution (recommended for severe buildup) or a 5-gallon jug of distilled white vinegar
  • A channel lock wrench

Water Heater Descaling General Guide

These are some common instructions. Again, double-check your owner’s manual before getting started.

  1. Set the water heater’s temperature to 150°F and let hot water run through the heater for about a minute.
  2. Shut off all the power to the water heater.
  3. Close the incoming and outgoing water isolation valves. If your unit doesn’t have isolation valves, then you can buy some and install them yourself.
  4. Have a bucket ready to collect water as it drains. There will be about a liter of water or so in the pipes of the tankless heater.
  5. Drain the unit and connect hoses to the drain ports of the isolation valves “A” and “B”.
  6. Dump this bucket or have another bucket ready to go with a solution to be pumped through the heater.
  7. Fill an empty bucket with a mix of one gallon of descaling solution and three gallons of water. If you are using distilled white vinegar, use between four and five gallons with no water added.
  8. Open the isolation valves A and B.
  9. Turn on the circulation pump. Let the solution circulate through the tankless water heater for at least 30 minutes, but an hour is better.
  10. Drain the descaling solution from the heater and flush fresh water through the heater by closing valve “B”.
  11. Open valve “A” with a hose leading to an empty bucket.
  12. Open up the inlet water valve to let freshwater flow through the unit and empty into the empty bucket to get all of the solution out of the heat exchanger.

Advanced Propane can help you get all the hot water you want when you want it with a new propane tankless water heater. Get in touch with us today to get started!