My neighbour has a boiler extract about a meter from my house, from which there is a steady smelly stream of steam! It smells poisonous - perhaps there is some carbon monoxide in the fumes. I can no longer sit outside my kitchen when their boiler is going, which is most of the time. Can I do anything? I have asked them to extend their pipe so that the fumes extract further up, but they have been told by their plumber that the boiler will then become too inefficient.
The plumber is right, the flu needs to be 'balanced' for proper boiler operation, but I'm sure there is a fitting that can angle the flu away from your house?
Sorry I'm not much use on this.