Noisy water flow after balancing rads

I have attempted to balance my system (old-fashioned vented) after reading the FAQ on this, but I find two puzzles: There is far more water flow noise in the pipes than there was before, it's quite objectionable; and I can't really get close to the 20C drop from inlet to outlet on any of the radiators without screwing the outlet lockshield valves almost completely down, especially on the rads nearest the boiler.
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Try turning the pump speed down a bit with the controller fitted to the side / top of it. It'll be marked, most likely, with 1, 2 and 3 on the dial, 3 being the fastest, so turning it down to 1 or 2 and trying the balancing again, should solve your problem.
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In an earlier contribution to this discussion,

You *don't want* a 20C drop! 20F (or 11C) is more usual. Is this the problem - that you're aiming at the wrong parameters?
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wrote:

That is true for a conventional (82 degree Celsius flow, 70 degree return) boiler, as is probably in use here.
For a condensing boiler, the heat exchanger supports a greater drop and 20 degrees is quite normal - for example 70 degree flow, 50 return.
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Thanks very much for these replies. It appears I misread C for F! I have turned the speed down to '1' and the noise has improved a lot. The fitter kindly left me the pump Installation manual many years ago, and in there it does advise setting 1 for most domestic systems. thanks again
Richard
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Did you read both pieces in the FAQ on balancing? The one at http://www.diyfaq.org.uk/plumbing/rad-balance.html explains the principles of this temperature drop, under "Principles".
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