regarding the Magnaclean, I have been fitting them to all Boiler replacement jobs since last November.
I don't have a powerflush machine but am considering making one from the bits I have acumalated in the workshop.
I try and get the old appliance to run so using it as a heater for improved chemical reaction on the magnatite, add a powerflushing chemical from a proprioty manufacturer and run it for three hours with a Magnaclean on the return. This procedure has produced good results so far.
The Magnaclean then remains, so preventing the plate heat exchanger to remain protected from any fine ferrous particles that would adversly affect the Domestic Hot Water out put, and, the warentee.
Some old systems are suprisingly clean.
If you are not in a mad rush your could do a Magnaclean on the return and put x400 in and run it for a four week period, with all rad valves fuuly open and run the existing appliance at its lowest setting when you are out to keep the chemical circulating 24/7 or at least 16/7.
Its very important that you thoroughly flush out the chemicles after the cleaning period.
One way to achive this if there is not a full bore drain point is to "drain, fill, run for 15 mins, drain, run refill, about four or five times.
That way you will have diluted any chemical that remains.
Tim
PS I use X800 for the three hour trip.