This Chattering(Buzzing) noise is caused by internal relay due to degrade of the electrolitic capacitors.
This fix als apply to Glowworm Ultimate 33FF and 50FF boilers.
Remove the control box and the PCB
Boiler PCB
This fix als apply to Glowworm Ultimate 33FF and 50FF boilers.
Remove the control box and the PCB
Boiler PCB