Also called a pressure differential change, this Chaffoteaux pressure switch is designed to discover whether the fan is operating and is linked to the Fan through heat resistant tubes right on the fan Venturies. This allows the boiler to discover if the fan is operating since 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 time gas could be transmitted to the burner along with the ignition procedure.
If the fan was to stop running there could be too little air flow throughout the air pressure switch that would create the air pressure switch to start. A sign would then be routed into the printed circuit board allowing the Chaffoteaux boiler to quit sending gas to the burner and also to turn off the boiler. The air pressure switch is a basic safety device ensuring that the secure functioning of the boiler.