I no longer do boiler replacements.
I have fitted loads in the past but I'm no longer registered to work on gas. I get plenty of plumbing work and I recommend others for gas work, sometimes they recommend me for plumbing work.
Spot on about BG.
A very good friend is a BG boiler engineer, he is very good at the 'job he was trained to do' what he doesn't know about repairing boilers and central heating isn't worth worrying about.
But he is now encouraged to sell,sell,sell and isn't happy about it.