Tankless hot water heaters may not have water tanks, but they still must be flushed regularly to keep them working at peak performance. Many tankless water heaters have indicators that will tell you when they must be flushed. Unlike water tanks, the problem with most tankless heaters is a build up of calcium. If you find that you are flushing your tankless heater more than once a year, you may want to consider adding a filtering system to remove some of the minerals in your hot water.
Step 1: Turn of your tankless hot water heater. If it is electric, turn off the circuit that services the hot water heater. If it is electric, turn the gas valve to pilot to prevent it from heating water.
Step 2: Look for the drain spigot at the bottom of your hot water heater. Attach the end of a garden hose to the end of the spigot. Direct the other end of the hose out of house to the yard, or into a bucket that can easily be emptied.
TIP: The building code does not currently require a clean out valve for many tankless hot water heaters. If you don’t have a clean out valve, call a plumber who will be willing to install one. The ease of cleaning and the money you will save by being able to clean the tankless heater yourself will be worth the cost of installing the spigot.
Step 3. Turn off the cold water shut-off valve to prevent water from entering the heater. Open the pressure relief valve at the top of the tankless hot water heater.
Step 4: Open the drain valve that is attached to the garden hose. Allow the sediment and other deposits to drain from the heater until water no longer runs from the hose.
TIP: Sometimes the sediment will be so thick it will clog of the hose or impede the flow of water. In this case, close the pressure relief valve and turn on the cold water valve. This should quickly flush the system. Turn off the cold water valve after a few minutes, then reopen the pressure relief valve to allow any remaining water to drain out.
Step 5: Close the pressure relief valve and the drain valve spigot. Detach the garden hose from the end of the spigot and clean any drips. Open the cold water turn off valve and turn on the electricity or gas to the tankless hot water heater.