1. Turn off everything that connects the boiler to electricity. From the two tanks identify the smaller one, which is also called the expansion tank or header tank. Turn off the water supply on the tank or block the ball valve. Verify that the ball has no water inside. The system can lack efficiency if the ball leaks in which case it will need replacement.
2. Identify the drain cock at the bottom of the pipe work and connect it to a hose secured by a jubilee clip. After that run the hose outside the house. Open the drain valve with a pair of pliers.
3. To flush the system faster, open all radiator valves starting with the highest level valves and advancing downwards.
4. When the water stops pouring through the hose check to see if the system is fully flushed. Not all water may have drained due to air in the system. If you notice this, open the ball cock in order to allow 6 inches of water to enter the tank. You should see the water draining through the hose in a few seconds. If the water isn’t draining due to an air lock, connect the other end of the hose to a cold tap and shoot water into the blocked radiator.
5. Close all bleed valves and the drain cock. Let the tank refill by releasing the ballcock into the expansion tank. Advance on bleeding the lower level radiators. Verify all valves to be closed properly.
6. You can now start the boiler running.
