Sounds like you have left it run too low 1 inch of oil left in he tank is probably not enough to gravity feed to the boiler I never leave mine run below 6 inches before ordering a refill, if you hadn't enough oil in the tank then your oil feed pipe has become air locked and will need to be bled to get the bioler working again for the next oil delivery.
"When you run out of fuel oil your boiler will often develop an airlock.
When you run out of fuel oil your boiler will have used everything in the pipe running from your storage tank. When you recieve a delivery of fuel the pipe remains completely empty. The air in the pipe will prevent the fuel from running towards your boiler, therefore preventing your heating from restarting.
The technique used to fix this very common problem is called 'bleeeding' the fuel line.
The process of bleeding removes the trapped air from the fuel pipe, allowing the oil free flow from your storgae tank to boiler."
You should be able to find instructions for bleeding the fuel line on Google.ie