Boiler replacment- building regs exemption?

pernes

I need to replace a potterton Flamingo boiler, which goes into an SE duct. I live in a block of flats 3 floors up I have had some plumbers (none of which have yet given me a quote, I assume they don't want the job as it is difficult) around all of whom tell me I can't use the exisiting flue and would need to run 10 1/2 mtrs of flue to my nearest outside wall, which means going through three rooms. I have read that some properties are exempt and can fit a standard efficiency boiler. I would like to have a Worcester Combi, which would go into the existing flue. I have been in touch with the building regs and they can't tell me how the points are reached for exemption and that the plumber will know, I thought they would be more helpful as I don't want to fall foul of regualtions. Found this info on another site "
The exemption formula is worked out on a points basis, with 1000 points being required to allow replacement with a similar back boiler. A mid-terrace house starts with a points score of 640, and a flat with 710. Moving the boiler to a different room with an outside wall (usually the kitchen) incurs another 350 points. If the property has cast-iron drainage pipes - which would be damaged by the acidic discharge from a condensing boiler - then it would be necessary to install a soakaway at ground level to accept the condensate, and this adds 100 points. Should the new boiler position require a flue longer than 2 metres, this adds another 200 points. So in many cases the 1000 points total is easily achieved".
Is this info correct? If so how do I tally up the points in my situation?
Many thanks, I'm getting confused more by the minute