hi guys, really struggling with a problem ive got on a myson velaire 50 70. Got called to a breakdown, and to cut a long story short, i've changed the oil pump and photocell, and got the boiler working. It fires first time every time but continues to lockout. the boiler can run for 2,5,10 even 20mins fine and then locksout for no reason, i dont believe it is locking out due to flame failure or poor running, because u can hear that the flame is still lit, and its only the lockout that make it go out. When it does lock out it does not go through its sequence to try and reignite (have tested this when the boiler is running by pulling out the photocell, and it goes through its sequence and re-fires everytime). I have tried a few different control boxs, and even a few different photocells to see if it made any difference, but the same. Im out of ideas, can someone help???