Possible causes include oil supply pipeline blockage, oil pump not pumping, oil supply pipeline vacuum leakage, etc. Unload the high-pressure outlet pipe to check the pump oil condition, normal pumping oil should be out of the oil column. Another reason why the nozzle does not spray oil is that the solenoid valve is not energized. When the oil solenoid valve is out of power, even if the oil pump runs normally, the high pressure end will not supply oil to the nozzle, only after the controller makes the oil solenoid valve energized to allow diesel ejection, its purpose is to prevent the original accumulation of diesel fuel in the furnace in the case of open fire deflagrate. Under normal circumstances, when ignition, the burner is pre-blown to clean the residual diesel oil in the combustion chamber, and then fuel injection and ignition. In the pre-blow stage, although the oil pump motor is running, the oil cut-off solenoid valve is not energized, and the high-pressure diesel pumped by the oil pump is cut off by the oil cut-off solenoid valve and cannot access the fuel injection nozzle.