Hi-Agilent technologies expert. I have installed a VHS-4 high vacuum diffusion pump in my furnace system. Recently the heater(1450w) of the pump stopped working and I replaced it with a new one . Also, I have changed the oil. But after giving the necessary maintenance treatment when I turned back the system on the High vacuum pump VHS-4 was not working e.g.no suction to 10^-6 torr. However, the mechanical pump working properly, but the heater is getting hot too as compared to the previous one. By viewing through the glass site window It was observed that the oil was splashing or boiling violently during the heating of the pump and showed a change in color. what caused it to malfunction and how to rectify it. I am waiting for your kind suggestions and remedial action Thanks.