On 2006-10-15 17:47:26 +0100, Jim D said:

On Sun, 15 Oct 2006 17:23:55 +0100, Andy Hall
wrote:

Thanks for the reply. It just occurred to me: scaling is only likely
to occur on the side of the heat exchanger that passes water from the
mains inlet to the sink taps, isn't it? In if that side was scaled up,
then there would be a reduction in flow from the hot taps, wouldn't
there?

Jim D

Possibly some, yes.

If the system is sludged, then a different course of action is needed -
basically clean it out and fill adding corrosion inhibitor to the
system afterwards

That's exactly what I did, a few days ago, just before this problem
started..

Jim D

Is it a sealed system or open vented with tank in the loft?

If it's the latter, then pumping over of heating water or sucking of
air into the system because the relative positions of pump,
feed/expansion and vent pipes can cause the water to become more
oxygenated than it otherwise would be. This effectively "uses up" the
inhibitor. You can diagnose this problem if the radiators need
frequent venting and the gas released is air and not hydrogen, or
pumping over can be seen from the vent pipe with the tank getting very
hot.

EIther way, I wonder if you have managed to flush some sludge into the
boiler....