I had my central heating oil boiler serviced last year, it had a
bearing replaced in the motor.

Since then it seems to burning a 'rich mixure', i.e. there is a very
obvious kerosene smell from the exhaust. And the oil fill seems to be
used quicker.

There is a mixture screw/valve in the side but when I tried to adjust
it the burner stops and refuses to start again of its own accord
unless I increase the mixture.

Is it the quantity of fuel or the lack of air? Or am I completely on
the wrong track.

I can't remember the burner model number but if it helps I can look it
up to-night.

regards

MJW