The Ferroli air pressure switch is a safety device which checks if the fan is working correctly. It ensures that, if the fan fails within the boiler, there will not be a build up of noxious fumes with no means of venting them. The printed circuit board closely monitors the air pressure switch to make sure it is fully functional before the unit is fired up, preventing the appliance from starting without one of its key safety instruments.

Brand Name	Ferroli