Potterton Air Pressure Switch (Aps) (Page 3)

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