HEX flush

Hi Tom and everyone hope your all in fine fettle, I've not been on for a while. anyhow my query is regarding my vokera boiler, plate HEX  was blocked up with crap a couple of years back and with help from Tom and the guys and a bit of research I managed to remove it and give it a quick flush with some spirit of salts, new seals and its worked lovely since  until recently its started to get the old symptoms back only milder, so im planning to repeat the process and I though i might as well give it a quick flush round with some X800 while im doing it, so my question is, is there any way I can syphon some X800 in to the primary heat exchanger, i thought maybe via the AAV on the pump and try sucking it in by releasing some pressure on my magnaclean filter ive fitted  if I isolate the flow.. all comments welcome guys even the piss takes ha.. cheers Flint