We have just completed a job in Godalming where we installed a thermal-store cylinder heated via a new condensing gas boiler. The obvious benefit of thermal-store is mains pressure hot water without the need for an un-vented hot water cylinder. However; another benefit is the ability to heat the thermal-store with other heat sources which can also assisit with the space heating demand.
Our customer chose a solar thermal-store enabling solar thermal water heating to be added at a later date. It also had the additional facility for a wood-burning stove to be plumbed in to it via a gravity system of pipework. Finally it had an eletric immersion heater fitted as a final back-up in case all else failed.
If you want to link different fuel burning appliances to the benefit of space heating then this is probably the best way of doing it.