Most tankless water heater manufacturers recommend an annual flush of the unit to prevent sediment buildup. While some people ignore this recommendation, it is important to remember that sediment can cause a number of problems for your tankless water heater, including: -Reduced efficiency -Increased wear and tear -Potential damage to the unit If you have hard water, it is especially important to flush your tankless water heater on a regular basis. Hard water contains minerals that can quickly build up in the unit and cause the problems mentioned above. To flush your tankless water heater, simply attach a garden hose to the drain valve and open it up. Let the water run for a few minutes until it is clear. You may need to do this a few times to get all the sediment out. While it may be a bit of a hassle, taking the time to flush your tankless water heater on a yearly basis will help prolong its life and keep it running efficiently.