On Tue, 21 Oct 2003 22:09:02 +0100, Dougie Nisbet wrote:

[ ... ]

switch off, release pressure at the release point.

connect fill and drain hoses, open drain valve, close pressure
release valve.

Turn on supply. Then by opening and shutting valves round the house,
you can send a fast stream of water through each rad in turn. This
should remove a lot of the sludge except if a rad is solidly blocked;
if so, then you will have to remove that rad and flush it.

I understand the fundamentals behind what you're saying but I'm struggling
with some terminology. 'pressure release valve' - is that the bypass valve
that connected CH flow and return just below the boiler?


Nah - I'll answer my own question. I presume it's the 'pressure relief
system' mentioned in the manual for my boiler (a RAVENHEAT RSF 100ET). I
can't get access to it without taking the cover of the boiler.