You will need to flush it out properly then add inhibitor, provided there's no leaks it should be fine.
It's been powerflushed twice - and all rads off and flushed as well less than a month ago + inhibitor - but the hex is blocked again.
Are you sure the HX is blocked on the system side, most unlikely if that filter has a gauze in it.
I would isolate the filter and check it's clean by removing the gauze, I would also check the pipe isn't blocked between the filter and the TF1.
agile was talking about a major corrosion problem we had in Bath that cost 100 of thousand quids, I assume the sparkies insurance paid.