Hi, we have a noise coming from our Glow Worm Micron 50FF, initially the engineer thought is was the fan, but after replacing that it is no better, it is a loud noise almost like a vibration noise / resonannce, it happens after the burner kicks in and he is now saying it could be the Gas Valve but he has never heard one so noisy, could this be the problem? It is lower down that the heat exchanger and the Burner Tray seems to be secure

John, July 2015

The next thing to change is your boiler engineer.

He has made a diagnosis of noisy fan and has changed it - you pay him for his expertise - not to guess.

The gas valve is a solenoid operated on off valve - hardly likely to make a noise - when he says he thinks it to be the gas valve then that's another guess.

Get yourself a wooden spoon and use it like a stethoscope to track down the source of the noise - your description of vibrating resonance suggests just that - a piece of the casing or exhaust ducting no longer secure.

Did he keep the old fan?

Good luck..., July 2015