Draining water from a boiler system requires turning off the power, hooking up a hose to the drain spout and using a bleed key in the connected radiators. Place the end of the hose in a sink or other suitable drainage location before opening the radiator.
When the boiler drain valve is opened, water emerges quickly and forcefully. The initial draining can take several minutes and does not empty the system entirely. Using a bleed key in each radiator reduces pressure in the system and forces out more water. Open radiators from the highest point in the home to the lowest. Upon opening the radiator with the key, there is a loud noise as the water exits. When the radiator is quiet, close the radiator. After all radiators have been opened and drained, close the boiler valve.