Thanks for help so far! ;
Update;
New replacement rad installed, yesterday then had the power flush with a kamco, used fernox f3 as the cleaner and f1 for the inhibitor.
followed the kamco instructions to the letter with the plumber,.
I bought a tds meter and when we were finished and the mains and CH water matched, also the PH was fine so will see what happens. (plumber borrowed the kamco from a mate)
I have a frenox system health kit to test it after ive ran it for a few days (lab report one) - should I leave it longer?
As you can imagine im acutley sensitive to any potential issues now, the heating was ran yesteray, all ok, bit of balancing needed etc.
came to run it again this morning and there was a fair bit of gurgling and bagning from the upstairs tall vertical rad (the replacment one) so I bled it and it seemed to stop.
running this morning all rads as heating up well
2 questions;
1) is the air in the rad a normal issue after a power flush and rad swap and if so how long should it take to dissapate (if Im still doing it in a week is that a sign of the previous problem - should it have settled down by then)
2) the tall aluminum rads make a whoooshing sound after they have been heated for about 30-40 mins and continue until the heating is switched off (not pops and gurgles, more liek the sound of a constantly running tap or toilet cistern filling up) - any thoughts on that. the issue was there before, since install so it may be a design fault rather than a system fault - just annoying.