Alpha CB24, CB28 Fan Assembly 1.017998
This Fan is the part in the boiler that removes all the carbon monoxide produced by the boiler and it is the part that provides the oxygen to keep the burner running safely. The fan is monitored and driven via the pcb on the boiler, on the older boilers the fan is connected to an air pressure switch via heat resistant tubing which connects to the fan via venturies that are located in the fan. If the fan fails to run the boiler will be shut off by the printed circuit board making sure no carbon monoxide can be created by the burner when the fan isn't running.
Most engineers change the heat resistant tubing that connects the fan to the air pressure switch because over time the tubing becomes brittle and can cause the boiler to fail. If you would like to purchase the tubing it can be viewed below and purchased below.