Oil not reaching burner?

Hi I have a Riello 40 series.
Ran out of oil some months ago and just got a refill. I have replaced the nozzle and the fire safely valve (thingy) as it was dirty. WHen I they to ignite the burner not happens.....it winds on for a short while then cuts out....I have checked to see if the fuel is coming through by loosing a pipe slightly, however not.......The pipe from the tank is clean as I tried syphoning....and it came through. I suspect something is not drawing the oil through.The pump is about a year old...but used may be 4 months of that time........can you help............I don't want to get an engineer out and get ripped off for sometime that I could do myself.....Help Please!!!