worcester Danesmoor 20/25, lockout/repriming tigerloop and pump?

The boiler has been working fine for years but I have recently had to re-route the oil feed line from the tank. I took the opportunity to do the service on the boiler and replace filter etc. I now have the situation where there is no oil in any of the pipework, the tigerloop or presumably even the pump. I have tried priming the system by running the start process from lockout about five times but unsurprisingly no oil is raised.
How do I bleed/purge the pump etc to get things going again. I notice there are a couple of large hex nuts on the side of the pump and also what looks like a bleed nipple which looks relevant?
The burner is a Selectos and the pump is a Sundstrand. I can supply photos for ID if necessary.
Thanks for your help in advance!