To quote you, "Note that if running the boiler from the genny you will probably need to make sure that earthing is correctly connected for the flame sensing to work properly. So basically set the genny up with an earth spike like a TT system, and tie one leg of its output to the earth."
Well, that turned out to apply in the case of my boiler, but why? Can you explain it slowly and simply? Why does the flame sensing need this?
Bill