Problems with my Worcester heatslave 15/19!?

I just put oil in the tank, 2 days later the boiler goes out. I had a guy come look at it and he says it was the water pressure. He fixes it and it turns on. I come back from work a few hours later and its off again and no hot water or heat. Can anyone tell me something else that might be wrong? The watchman downstairs is reading (r) if that means anything but there is definitely oil in the tank. Could it be a oil problem?