Had this issue a few months back on a quote
The existing boiler can be moved within the original footprint of the building, but not into a new extension as this falls under current building regs which don't allow non condensing boilers to be fitted
So therefore, if it was moved into new extension it wouldn't comply with building regs
I lost the job as I wouldn't move the existing boiler, only replace with new
No doubt they found someone who would
PS the above mentioned job was in the rear of a church building and they were made aware of regs etc, but still looked for the cheaper option