A friend of mine is trying to sort out a problem with her boiler. It is a Worcester Heatslave 15/19. She recently ran out of fuel and on refilling the oil tank, the boiler kept locking out after around 15 mins. I have had a look and oil is getting to the pump. I have vented the pump to ensure there was no air and all was fine. However, I also found that the CH pressure safety valve was operating and the gauge was at 3 bar. The water wasnt pouring out, but a steady/slow flow was present. I then found that the filling loop had been left open (for several months!!). I have switched the filling loop off and the pressure is now at around 1.25. It doesnt matter whether DHW or CH is individually calling for heat, the boiler still locks out after around 15 mins. Any ideas?