AIUI any new or replacement boiler will have to conform to all parts
of the building regs, but particularly Part J, Combustion appliances.

http://www.planningportal.gov.uk/eng...documentslist/

So yes, much more than just Part B, Protection from fire.

Either a building notice to your local building control dept is
required, or an approved person that can certify compliance.

I don't know if your qualifications covers it, but as you're not
familiar with the regs, I guess you don't usually work on installing
domestic gas boilers.