DavyJones,
House is a bungalow, oil boiler powers 3 beds, 1 bath and 1 cloak (all with 1 rad). Back boiler fires living with 2 rads, kitchen with 2 rads and hall with 1 rad.
Pretty sure the system is vented.
Finally, i'm not too sure re. the cylinder / if they meet here etc but there is only one hot water tank in hotpress, if this helps any?
Apparently the house was originally two seperate houses!