Shut off the power to the central boiler at the main fuse box for the home. If the boiler is gas powered, turn the gas line valve off and extinguish the flame. Turn off the automatic feed from the water line.
Screw a drain hose to the boiler drain opening and screw a separate hose to the boiler return drain. Extend the free ends of the hoses outside or into a tub drain or bucket.
Twist the knobs above each drain counterclockwise to open the drains and allow all of the water inside the boiler and heating system to drain out. When the boiler is empty, twist the knobs clockwise to close the drains.
Open the automatic feed to refill the boiler with water until it is approximately half full.
Mix a 2 percent solution of radiator scale cleaner in a bucket using the instructions on the cleaner packaging. In general, you will use approximately two liters of cleaner for every ten radiators in the home or building. Pour the solution into the boiler via the feed valve.
Turn on the system and allow the cleaner to circulate throughout the home's pipes for approximately 30 minutes.
Open the feed valve to fill the boiler up to capacity with additional water.
Allow the solution to continuously circulate in the system for 48 hours. If you are using the system as normal, allow the solution to circulate for seven days.
Drain the system completely of all water and de-scale cleaner as done previously. This washes out all scale from the system. Close the drain valves and open the feed valve to refill the system with clean water. Drain and fill the tank twice more, for a total of three drains and fills, to ensure that the process removed all debris from the boiler.
Begin using the system as normal.