What to check if a boiler is working but with visible smoke?

If an oil boiler is working but there is visible smoke from the flue or a high smoke number, heating engineers should check the following. Please note, it is important to always isolate the electricity supply to the boiler before working on the boiler. 

• Check whether there is insufficient air supply - check the air damper setting and the condition of the fan.
• Check that the room ventilation is adequate - please refer to the Boiler Installation Manual.
• Check the nozzle size and type.
• Check the fuel pressure which may be too high - please check and adjust if required.