Grant Euroflame boiler with Riello RDB Burner no longer lights?

We hadn't used it in a few months since we ran out of gasoil, but I finally got some the other day and started it up. It seemed to work fine for a couple of days after that, it took a while to light and stay lit though; usually lighting several times. But a couple of days later I turned it on and it fired up okay but after half and hour or 45 mins it cut out and the reset light came on. It pretty much went on like that for the next day until yesterday, I cleaned the boiler out thinking some soot might have built up in their and was hampering its ability to fire, but it wasn't as bad as I thought it was.

I put it all back together and turned it on, pressed the reset button - I heard the motor start up, a few seconds later there's a click, but instead of hearing a roar as it lights which is what it had been doing, I just hear the motor running for a few seconds then it cuts out.

Bleeding it didn't work. And I even tried giving the electrodes and injector a quick clean with some wire wool but that didn't work either. It is getting fuel I know that much. I'm just at a bit of a dead end as to what is exactly wrong with it.