This Genuine Worcester Bosch Product for the 15Sbi Boiler
The Air Pressure switch is a Safety device which checks the fan is working accurately.
It ensures that, if the fan fails inside the boiler, the boiler would not be allowed to start to stop a build up of dangerous gasses with no means for expelling them securely.
The printed circuit board checks the Air Pressure switch is working to guarantee it is ok for the boiler to fire and not if this key part isn't working.
