Further to another thread, I've been looking into having my new boiler
fitted with weather compensation controls.

I'm still waiting for the engineer's quote for this but am confident
it's going to be very expensive. My question is, to which I'm unable to
find an answer, is what sort of fuel savings is this likely to make?
Although our gas bills in this old and poorly insulated property are
sky-high, I'm sure it won't make economic sense to fit this gizmo unless
it makes a reasonably substantial saving. All th blurb I can find is
very cagey on this point.

(I'm going for a W-B 30CDi system boiler, and this is the weather
compensation device:
http://www.worcester-bosch.co.uk/cache/file/289/fw100-installation-and-user-instructions.pdf

Secondly, the engineer's pointed out that if I have this fitted, I need
to be aware that the boiler will always prioritise HW over CH, so it can
take quite some time for the CH to kick in if the HW is sold. (I think
this is due the tio the diverter valve it needs? not sure). How much of
a real problem is this?; but anyway I thought that was how all/most
systems operate?

Thanks for any advice
David