I have no gas qualifications, and no gas experience, but I know the basics of combustion, which you don't appear to have any understanding of. Even I know what the black sooting is - it's obvious. Quite honestly it beggars belief that someone who is qualified to work on gas in any way doesn't understand this.
I am quite rightly not allowed to work on gas, but you are. This is not at all reassuring!
I am quite rightly not allowed to work on gas, but you are. This is not at all reassuring!