first, replace the oil filter cartridge. if this has already been done, have your technician check the oil pressure of the oil pump on the water heater without furnace on and again with furnace running. a plugged pump strainer or weak oil pump could also cause this problem. have him check ALL the oil line fittings and make sure they could not be causing air to enter the system. a worn oil pump can also allow air to enter system if it has to overwork itself to provide oil. darren