Upon arrival u it was off. Customer stated the oil tank was empty and they got a delivery the other day. Bled oil line and saw some sludge. Checked the nozzle and found heavy carbon buildup on the nozzle and nozzle assembly. Cleaned the carbon buildup and replaced the nozzle. Slightly adjusted the electrodes. Bled the oil line again and started the boiler. Performed combustion test and adjusted the air and fuel. Unit was running at 5.6%o2 45ppm co. Added oil sludge additive to the oil tank and had customer verify the oil fill cap was on the pipe.