I asked for it...
First pick a chemical. Middle choice , Fernox Heavy Duty Restorer for a week, or Sentinel Ferroquest for a couple of days. There are others, such as Kamco's. Look all over their site for background reading.
Sketch out your system to see what's where. IE you need to know if it's a gravity system, fully pumped, uses a primatic cylinder
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Easy way to do it is to connect at convenient rad valves having removed the rad. Garden tap connectors usually fit onto the valve unions. It would be better to put a T in each of the flow and return pipes rather than going through a restrictive valve, but hey. How good is your mains pressure/ flow?
You have to cap the vent pipe, and the feed, or connect them together. Use a small magnet round where the feed pipe joins the system to try to find magnetic scale inside the pipe. If you do, you may have to cut out the pipe and replace it.
Check what motorised valve(s) you have. In the Manual position they will be open. With a 3 port yo won't be able to shut the cylinder loop unless there's an extra gate valve - consider fitting one (£2-3)
Assume all the rads are in parallel, and the boiler will be too. Open just one rad at a time and and the mains through until no more black stuff comes out. Banging the rad helps. Reverse the pipes to see if more comes. With all the rads shut you're flushing the boiler. If you close a pump valve you'll shut off the boiler so it isn't short-circuiting the rads while you're trying to clean them.
If you're still with me I'm sure you can work it all out! Read all the instructions, flush the chemicals out then use an inhibitor such as by Fernox or Sentinel.
