Well surely if you've fitted a boiler for someone that makes you an expert,so why ask us for answers,the fact you refer to hydrogen as nitrogen tells me you know very little and shouldn't be fitting boilers.
Sounds to me like poor ole KBS is either a DIYer or a complete imbecile carrying out work he knows very little of. Does KBS stand for Knows Bull ****
Nearly burnt your arm off, are you sure you haven't plumbed the gas supply into the water supply somehow.
Yes your right, today we did extra lessons. Knowing the difference between a Gas and a Liquid, sounds like you should join me next time I go.