I am not a plumber either.
It is said that old sediment can clog a new boiler. It will certainly not do any good.
I've been very pleased with the Magnaclean I fitted to my mother's old system during the summer.
I started by bailing out the sludge from the F&E and moped it clean, replaced the ballvalve, and added a new lid and jacket while I was about it. I also fitted a full-bore drain-off for more through and quicker draining, and put lockshields with drainoffs on a couple of downstairs rads, and replaced a few worn, leaky or jammed valves and bleed nipples.
I did a plain-water flush and drain, then fitted the Magnaclean and let it trap all the loose sediment. This took a day or so. When the water was clear, I added X400 and it collected a lot more. It's now declined to about half a teaspoonful per week. I drained out the X400 and added X100 after a couple of weeks, however I have since learned that you can leave X400 circulating indefinitely, according to the makers instructions, and the Magnaclean will continue trapping whatever black sediment is loosened and circulating.
You have to add inhibitor and check for piping defects to prevent future corrosion.
It does not trap limescale, dead spiders etc so it is worthwhile doing a plain flush and drain to get them out. It is not as quick as a powerflush but I am satisfied that this method has taken out all the loose stuff, loosened a lot more, and the circulating water now looks very clean. It is no longer creating gas and does no need to be bled any more.
It took me a Sunday afternoon to do the fitting and draining, another to drain it off and change the old valves and bleed nipples which I had identified on the first visit, plus a few minutes to check and empty the Magnaclean whenever I call in.
