Also known as a membrane, it is a boiler part that is normally located within the diverter valve or hydraulic section of the Biasi boiler. Its main purpose is to move a pin that then operates a micro switch which in turn sends a signal to the printed circuit board. The signal is normally to indicate the pump is running or there is a demand for hot water. They are sometimes referred to as the pump proving ? flow diaphragm or the domestic hot water DHW diaphragm.
Biasi BI1011111 Pressure Switch Disc (CH)

Part: BI1011111

Price: £8.71
Biasi BI1011114 Pressure Disc (DHW)

Part: BI1011114

Price: £13.65