Thanks for the reply.
In your experience have you ever come across a board that buzzes in this manner? Its really loud, I actually thought the boiler was fitted with a buzzer!
There's no spark at the electrodes and its the board that feeds them that is buzzing, so I have made the leap to the...
Biasi M90F has stopped working.
Steady pulse from standby light.
When requesting CH or HW it starts buzzing - one second of buzzing, stops buzzing, then one second of buzzing. Over and over and over.
Took control panel apart and there are two pcbs. One on the right has a relay in the middle...