Power flushing is a term used for the process to forcibly clean a heating system at a high velocity & low pressure, the process is made more effective with the use of powerful cleansing agents. The objective is to restore heating system circulation and cure noise problems. Power flushing removes sludge and corrosion deposits in the heating system, a flushing machine should be used on an old heating system prior to installing a new boiler.
Modern compact condensing boilers are prone to problems caused by debris in the heating system water. A new boiler can malfunction if the system it is going to be installed on is not cleaned prior to installation. The heat exchanger may become blocked or even worse split, resulting in your manufactures guarantee becoming invalid.
It is a false economy to not have a power flush as the damage caused will cost considerably more than the initial outlay.