Ariston Air Pressure Switches
Also called a pressure differential change, this Ariston pressure switch is designed to discover whether the fan is running and is linked to the Fan via heat resistant tubes directly on the fan Venturies. This enables the boiler to detect if the fan is running because air flow from the fan shuts the air pressure switch which then sends a signal down to the printed circuit board (PCB) confirming the fan is operating. At this point gas can be transmitted to the burner along with the ignition process.
If the fan was to jam there would be too little air flow across the air pressure switch which would create the air pressure switch to open. A signal would then be sent to the printed circuit board allowing the Ariston boiler to quit sending gas to the burner and to turn the boiler off. The air pressure switch is a basic safety device ensuring the safe running of the boiler.