Andy Hall wrote:
We've had this conversation before.
The correct approach is prevention, not cure.

Absolutely.
Getting involved in trying to rectify the problems caused by neglect of
chemical water treatment on any heating system and you rapidly learn
the meaning of the phrase "false economy".

Sadly applicable in many of the UK's public institutions where short
term penny pinching by ignorant cretins in sharp suits has caused
billions of pounds of irrepairable damage.

Doctor Drivel wrote:

Make sure the drain
cock is opened before the mains is turned on as too much pressure may pop a
corroded rad.

Or put a pressure reducing valve ( set to say 1 or 1.5 bar) on the
hose connection so that you can't over-pressurize the heating system if
something blocks the drain cock. I much prefer this, but I've
accumulated a few pressure reducing valves.

You can also get chemical additives called, or containing, flocculants
which, as it was explained to me, coat the sediment particles and make
it more likely that they will be entrained by the water flow and so
collect in a filter. Wikipedia explains them thus;

" Flocculants, or flocculating agents, are chemicals that are used to
promote flocculation by causing colloids and other suspended particles
in liquids to aggregate, forming a floc. Flocculants are used in water
treatment processes to improve the sedimentation or filterability of
small particles. For example, a flocculant may be used in swimming pool
or drinking water filtration to aid removal of microscopic particles
which would otherwise cause the water to be cloudy and which would be
difficult or impossible to remove by filtration alone."

I think Fernox do something, or else the power flushing chemical
suppliers. There's a danger of shifting the sediment from one place
(pipes) to another where they're much more harmful (boiler).