We have just a bought a house which we are getting ready for renting out. There is currently a Baxi wall mounted boiler in the kitchen which we would like to get rid of and put a combi boiler in the existing airing cupboard upstairs. In the airing cupboard there is a stainless steel flue from the downstairs gas fire, about 6 inches diameter, going up through the loft and through the roof. My question is... would it be possible/legal to link in the combi boiler flue to the gas fire flue to save having two flues going through the roof. There is no outside wall we could use in the airing cupboard. All comments would be much appreciated.