I have just had my boiler replaced after 22 years of having a gravity fed
C/H system I now have one that is mains pressure (filling loop / gauge). I
have 2 radiators that have been sluggish and hoped that the higher pressure
could improve the situation. It hasn't.
Today I tried:
1. Close both radiator valves and open the drain cock in the valve to
release residual pressure in the radiator.
2. Open lockshield on one end - got a full gush out of the drain cock.
Closed it
3. Open TRV at other end - only get a trickle. Turned it on and off a few
times - got some black particles out. Minor improvement maybe.


Any suggestions? Should I persevere weekly in the hope that if it is due to
crud in the pipe it may eventually soften and get flushed out? Access the
manifold and give the pipes a bit of a rattling about in the hope of
loosening something?

The system did have a X800 cleaner in for about a week before the boiler was
changed. It now has X100 in. Not sure when the problem started - it was
certainly some years ago when I noticed it. I suppose it could even be a
bruised pipes from the original build. The pipes are under chipboard floors
so I can't easily change it.

Any tips or tricks?