Tools You'll Need
Step-by-Step
Turn off the unit
Turn off the power (electric) or gas valve. Follow the manufacturer's shutdown procedure.
Connect the pump and hoses
Connect a hose from the cold water isolation valve to a bucket with the pump. Connect another hose from the hot water isolation valve back to the bucket. This creates a loop through the heat exchanger.
Open the isolation valves
Close the main water valves and open the service valves on the isolation valve kit. This redirects water through the pump loop instead of the house.
Run the descaler
Fill the bucket with descaler (vinegar or manufacturer solution). Turn on the pump and circulate the descaler through the heat exchanger for 45–60 minutes.
Flush with clean water
Disconnect the pump, reconnect the hoses to a drain. Open the cold water supply and flush clean water through the heat exchanger for 5 minutes to remove the descaler.
Restore and test
Close the service valves, open the main valves, remove the hoses, restore power/gas, and test the unit.
WHEN TO STOP
- If your unit doesn't have an isolation valve kit, stop — one needs to be installed first.
- If you're not comfortable working with gas or electrical connections, call a plumber.
- If the unit displays an error code, note it and call a professional.
WHEN TO CALL A PROFESSIONAL
- Most homeowners hire a plumber for annual tankless flushing — it requires the right equipment and procedure.
- Your unit doesn't have an isolation valve kit — one needs to be installed.
- The unit displays an error code or isn't heating properly after flushing.
- You're due for annual maintenance and want it done right.