I have had a call from a customer to say her boiler is making a popping sound and it turns out, she has not been able to hear it but her friend said its being doing it for a while. I was sent a video of the boiler, showing the flame through the window. Main flame looks good but it looks like the pilot goes out then relights? I am going to have a look on Monday. She said it was serviced a couple of years ago, her friend said she had been hearing the sound for quite a while. Anyone come across this before? I would like to go in with some useful knowledge. Thanks