I have been given two quotes for a boiler replacement both of which require a 28mm pipe gas supply. The meter/mains supply is at the opposite end of the house to the boiler. A 22mm pipe runs into the outer wall and ends up at the boiler, route unknown. At some point it feeds a gas fire and a hob before hitting the boiler on a 15mm pipe. Gas safe engineer 1 thinks it goes through concrete floors at ground level and engineer 2 thinks that it runs under the first floor floorboards across the house. Engineer 1 wants run a fresh 28mm pipe right from the meter to the new boiler (partly on the outside of the house) which i want to avoid as it will look ugly. Engineer 2 wants to tap into the 22mm pipe as it enters the house through the wall at first floor level (approx 3m run from the meter). My questions are: 1. Is tapping a 22mm pipe and running 28mm of it 3m downpipe ok to do. Will the boiler run ok? 2. Is there a way to actually work out where the existing 22mm pipe runs? 3. Is it even possible to run a 28mm fresh pipe through the cavity wall vertically up to first floor (and then send it under floorboards across thd house)?