How squint is squint? If it's a few degrees off, I can't imagine it can make any difference at all ( I'm guessing, mind ). Are you sure you aren't smelling the initial waft of unburned gas that always happens when the boiler flashes up, coming out of the flue that is. If you're in a room sealed away from any chance of smelling the flue fumes then I'd be concerned. You can buy tester spray to check for leaks, I'm told squeezy can be corrosive if you don't clean it off properly. If in doubt, get the CORGI man back in.
Andy