Thanks to all for your replies. We have gone with the recon burner
unit as it seemed the most cost effective solution. This has worked a
treat and also given us a quieter boiler. I am now convinced that our
old pump HAS to be gravity fed - so it simply wouldn't suck the oil up.
I think if the tank would have been full, it may have worked - until
it was half full again!

cheer

Jeremy