Humming noise from Glowworm Flexicom

[GQuigley67]

went to see this boiler today, customer showed me it on heating and it made a humming noise when it was on, i serviced it then fired it up agian and it made this noise for a while then stopped, but when it was making the noise when i took the front case off it didnt make this noise though. Any you more experienced guys know what this is ?? its a sealed gravity fed system

 

[Steve @ TheHeatingHub]

I dont really know which isn't a use full I know but only thing that jumps to mind is if the case is off and no noise perhaps some kind of air/gas mixture (flue problems maybe)? sorry I couldn't be more help

 

[AWheating]

possible flue issue, or loose case causing vibrations?

i went to a boiler once that was humming and locking out. It had a wasps nest inside it, mate had been on holiday for 2 weeks and while he was away they built a little house inside his boiler.