On Sat, 20 Nov 2004 21:12:25 +0000, "Ed Sirett"
wrote:

Sorry I have now read the OP properly.
The combi is working correctly and the 'feature' does occur on many
models.

I'm familiar with several models although some models might not exhibit
the problem though most do I would guess. A model name would help here.
In fact the only ones which I reckon are ones with a sperate internal
bypass pipework.

On many models the secondary heat exchanger also serves as a part of the
bypass ciurcuit. This is easily implemented by arranging for the
diverter valve to bleed primary water through the secondary heat exchnager
when in CH mode. So in winter the 2ndry HE gets to the temperature of the
primary flow. This means that the contents of the 2ndry HE are hot, this
slug of very hot water will comes out first in DHW mode.

To mitigate the problem try turning the radiator tempertaure down.
Of course if the rads are not over sized then the house won't get
heated. 8-(.

All the boilers which have double primary heat exchnagers (eg Ferolli)
or integral tube-in-tube type like (Pott. Lynx, Saunier Duval)
will also have this problem and likely a worse version.

Hi,

Does it bleed water regardless of the flow in the primary and can it
be blocked somehow? If there is a differential pressure valve in there
or it can be blocked it may be possible to use a lower pressure one
elsewhere.

cheers,
Pete.