Hi Jsgas58gas, In answer to your question if the boiler has a low pressure switch you can throttle back the return valve on your machine, assuming it produces enough pressure like the Fernox unit does, which will apply pressure across the boiler enabling it to be fired up.
FD Powerflow, agree whole heartedly, Magnacleanse system does very little to clean a system other than remove the loose material already circulating, efficiency of clean is less than 50%, Powerflush with the right chemicals and achieve an efficiency of clean around 95%+!