Was looking at possible positions where someone could site a new boiler... There is a nNice space on the wall in the kitchen which would be ideal (above where the old floorstander boiler is currently fitted). However there is a partially removed chimney breast on the outside of the wall that is in the place the flue would normally exit. (its corbelled out from the wall about 5' off the ground, and then continues up to a normal chimney stack).
So I said that they would probably need to have an extra extension in to boiler flue to run half a meter to the side in the kitchen first, before turning and exiting the wall in the normal way so as to miss the old chimney stack.
That got me wondering though, although it does not seem "right" I can't put my finger on any rule for not sticking the normal flue right through the old stack - its completely unused and only about a foot deep. Can anyone think of a reason?