Firing problem with Myson Velaire Vitesse oil boiler

Does anyone know the correct setting for the air damper on the Riello 40 G7X burner of a Myson Velaire Vitesse 60/80 burning 28 second oil? An 'engineer' - who fiddled about then admitted he did not really know what the fault was - moved the aperture and it has never worked properly since. I want to check the aperture is correct before I check the electrode settings in the combustion head. The boiler often fails to fire up automatically, but starts after the reset button has been pressed a couple of times. The fault finding chart in the manual suggests the electrodes may be sooted up but also makes it clear that the air damper setting is critical to clean burning. Thanks in advance. Tim
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Give these people a shout and ask them if they can help :
http://www.rielloburners.co.uk /
I'm sure they should be able to give you more advice on this.
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