Biasi Air Pressure Switches
Also known as a pressure differential switch, this Biasi pressure switch is designed to detect if the fan is running and is connected to the Fan via heat resistant tubes directly onto the fan Venturies. This enables the boiler to discover when the fan is operating because air flow from the fan closes the air pressure switch which in turn sends a signal down to the printed circuit board (PCB) confirming the fan is running. At this time gas can be transmitted to the burner along with the ignition process.
If the fan was supposed to quit running or jam there would be too little air flow throughout the air pressure switch that would cause the air pressure switch to open. A signal would then be routed to the printed circuit board allowing the biasi boiler to quit sending gas to the burner and to turn off the boiler. The air pressure switch is a basic safety device ensuring the secure running of the boiler.