Riello 40 not firing?

Hi,

I ran out of oil during the night and turned off the control panel in the morning. I got oil delivered, turned the control panel on (indicator lit) went out to reset the boiler and there was no reaction. I went back in to check the control panel and the display was off. I changed the battery, but the indicator wouldn't come on. I replaced the unit with an indentical model and the indicator lit. I went out to reset the boiler and it wouldn't fire. Assuming an airlock I opened the nut to bleed the air, but no air came out only a dribble of oil. The boiler doesn't make any kind of roaring noise then cut out as expected, just and electrical hum followed by a click. The oil pump and motor were replaced about two years ago. Could anyone give me any advice before I have to call an engineer?

Thanks

Colm