I did discover the main reason for the cost was rebuilding a flue in the middle of the house and getting ventilation back to the boiler. He tried to keep the boiler in the same place. In the end we moved the boiler upstairs into a cupboard that was already there and was fitted on an outside wall next to one of the bathrooms. Again this proved a very easy solution for the condensation. I have to admit it does depend on the chap that comes to give an estimate. Obviously some are switched on and are looking how to cut costs others are just plodders and don't use that organ between their ears. I did do a lot of research to work out what was possible and felt quite knowledgeable by the end of the whole process. I know one of my neighbours in exactly the same style house did pay over £8,000. He did get British Gas to do it for him. I knew there would be a lot of movement in prices. I think the main thing is to ask others, do research and keep getting quotes until you feel comfortable.