In article ,
"Matt G." writes:
Hallo.

We have two roughly 6" square air vents in the kitchen wall, one near
the ground and the other a couple of feet up. There used to be an
oil-fuelled boiler in a concrete cupboard in the kitchen, but now the
only thing that needs ventilating in that room is the gas hob. Would it
be ok to brick up one of the vents, as they're quite draughty, or does
the hob really need that much fresh air?

Check the hob installation instructions. It will say what the
minimum size of room is without having permanent ventilation.
If it's just a hob, I doubt there's a problem unless the
kitchen is small. If by 'hob' you meant a cooker or your 'hob'
has lots of burners or a very large burner with a flame failure
detector, then it will be a different story.

--
Andrew Gabriel