"Tony Bryer" wrote in message
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On Sat, 05 Jun 2010 09:54:27 +0100 Dave Plowman (News) wrote :
Did you clean the system properly as per the boiler maker's
instructions?

Yes, it was run hot with Fernox flushing compound, then after pulling
out the old boiler I connected the mains to the CH flow, turned off
all the rads then went round them in turn turning one on at a time so
the full flow was through that rad.

That is a good method. But. When the water comes out clean, turn down the
rad valve. This makes the water run through the rad at a higher pressure and
just along the bottom section, shorting out from valve to valve. It is like
pinching the end of hose and the water goes further. It then gets the sludge
collected at the bottom. That stuff could have still have been inside the
rads at the bottom.