My Rayburn has been working well for ages and although old it is regularly serviced. Now it has decided not to fire up on the boiler side, cooker works fine. I have had my usual engineer look at it but he has not been able to find the problem and says it is beyond him. The thing that I think should narrow down the cause is that the lock out light on the control box does not come on when the boiler fails to ignite. We have changed the control box but this has made no difference. Any ideas?