Upon arrival unit was off on reset. Pushed the reset button and the unit fired right up. Checked oil flow and had good clean flow with no air. Checked the nozzle and found carbon buildup starting to form on the nozzle and electrodes. Also found oil residue in the blast tube indicating the nozzle had been dripping. Replaced the nozzle and started and tested the system. Unit is working properly. Had hot water coming back on the return.