Have 3yr old potterton statesman 50/70 oil boiler,is smoking badly(black).boiler service & cleaned,burner checked,new nozzle and pump assembly fitted,oil lines clear and bled,pump pressure reset.flue gas temperature v.high. flame vivid yellow very ragged,mixture is obviously very rich but no adjustment to air damper seems to work for long. any ideas very welcome.

SOURCE: Burner adjustment

HE PART YOU REFER TO IS THE BAFFLE, TURN IT UNTIL YOU GET A BLUE FLAME

SOURCE: Gas Hob Flame

Hello
Tha sounds to me like the air mixture nedds to be adjusted on the stove, It's not difficult to do, just rotate it until the flames loose the yellow or your pans will be stained with soot.
The should be by the fittings (convertion fittings), you know?
LP Gas to Natural Gas or Natural Gas to LP Gas.
Hope this help
Eddie Rentas
Tupper Lake NY

SOURCE: My oil boiler is a

The actual final solution was to replace the fuel valve/solenoid following which the boiler has run without failure.
The conclusion was that the fuel valve solenoid was ok when cold but when heated up had some sort of electrical breakdown in its coils, causing the fuel valve to fluctuate until the boiler locked out.

SOURCE: Repressurise Potterton Performa 24 boiler

hope this is helpful. On my potterton 24 combi boiler it is the valve that sits the lowest, with a slight indent in the black tap. if you turn this for a short period you will hear a hiss and the pressure will quickly build to the desired pressure, when you can them turn the tap back off.

SOURCE: gas pressure washer

I have the same problem with a Karcher 2400hh.
Go to: http://www.wmpcs.com/index.php?main_page=page&id=14
they have the best diagrams and answerss that I have found.