My oil boiler has developed a problem, it will run for about 5 - 10 mins, the oil pressure drops to zero, flame goes out. fan continues for about 10 secs, about 10 secs later the trip light comes on. The fault finding chart for the 830.3 control box pointed towards a flame sensor fault so I have replaced the flame sensor and control box but the problem persists. I tried bypassing the thermostats but that made no difference. Oil pressure holds steady at 115psi whilst running. Any ideas as there's not a lot left to replace.