Andy Hall wrote:

Snip

The first thing is that you need to thorughly flush out the sludge and
solids.

There are two reasonable ways to do that:

- Drain system, remove radiators, take them outside and flush them with
a mains hose or pressure washer. Flush water out at each radiator
position.

- Power flush the system. This can be done by paying someone N x
hundred ££s or by renting the equipment and DIYing it.

Just what is a power flushing machine? can a pressure washer be adapted
to do the job?

Dave