These systems tend to have lots of sludge in them as they are open to the atmosphere (oxygen). The procedure is more complicated as the feed and expansion tank has to be isolated and there are various valves to operate, etc. Power flush companies tend to charge more for flushing these systems, over sealed ones.

The common optional extras on power flushing this type of system:

• Cutting out to clean or replace “the H”. Its gets blocked with hard sludge that power flushing does not always clear.
• Changing pump (they tend to get burnt out by the H being blocked)
• Changing 2-port or 3 port valves
• Changing radiator valves