Due to a small amount of intermittent kettling on a combi boiler I had Sentinel X400 system cleaner circulating around the central heating for the last 3 weeks, which I flushed out this afternoon.
Whilst it was all drained down I used the water filling tap on the boiler to flush it out further with noticeable black deposits appearing, did so until it was clear. The Magnaclean should pick up anything else in the CH.
After a second full flush, I topped up with Sentinel X100 inhibitor and no sign of any noise on the boiler and it's heating the hot water to a higher temp, another strange trait from before was when supplying hot water the boiler would cycle on off briefly approximately every minute or so which I think was a result of one of the temp sensors on one of the heat exchangers getting to high, causing the boiler to cut out, probably through reduced flow because of a small blockage, which it now no longer does. So all in all well worth doing.