How to Descale a Tankless Water Heater

What You'll Need For This Project

1. Shut off the gas and turn off the heater.

First, ensure that you have shut off the gas supply to your water heater, if applicable. Then, power off the tankless water heater by unplugging it.

2. Shut off the water valves.

Locate and shut off the hot and cold water isolation valves and then the service valves. Remove the caps from the service valves and leave the valves in the off position.

Note: By shutting off the isolation valves first, you keep the tank isolated from the rest of the potable water system.

3. Prepare the descaling solution.

Mix one quart of Hercules Haymaker Tankless Water Descaler and one gallon of water into the bucket.

Note: Do not operate the pump in less than 5 pints of liquid.

4. Attach the hoses.

Connect one hose end to the pump and the other end to the cold water service valve on the water heater. Place the pump in the bucket and remember to put the filter over the pump intake to prevent damage.

Attach the second hose to the hot water service valve and place the free end of this hose into a bucket.

5. Open the service valves and start the pump.

Open the service valves on the water heater. Turn on the pump to circulate the descaling solution through the water heater. Allow it to run for 30-45 minutes. Ensure the bucket has a minimum of 5 pints of water in it the entire time.

Disclaimer: Ensure the pump is plugged into a grounded outlet to avoid shock or pump damage. 

6. Flush the system.

After the descaling cycle is complete, turn off the pump and close the cold service valve. Disconnect the hose connected to the cold service valve. Discard the solution and refill the bucket with clean water.

Reconnect the hose to the cold water service valve, then open the cold isolation valve and flush the system for 3-5 minutes. This helps remove any remaining descaling solution. Empty the bucket as needed throughout the process.

Note: Once complete, the water should read near PH 6-8.

7. Reconnect the system.

Close the hot and cold service valves. Disconnect the cold service hose and resecure the service cap. Disconnect the hot service hose, and resecure the service cap.

Then, open the hot and cold isolation valves.

8. Restore the power and gas.

Turn on the gas supply. Restore power to the water heater by switching on the electrical circuit breaker or plugging it back in.

Note: It’s good practice to mark when you last descaled your water heater. Depending on your water hardness and usage, it's recommended that you descale your tankless water heater every 6 to 12 months.

9. Run a final test.

Run hot water from a tap to ensure the water heater is functioning correctly and that there is no air in the system.

Following these steps, you can keep your tankless water heater running efficiently and extend its service life.