Fans are fitted to gas boilers to ensure all the burnt products such as carbon monoxide CO2 is removed from the boiler to the outside safely. The fan also brings fresh air Oxygen into the boiler to enable the boiler to burn the gas safely. The fan receives its voltage and is driven from the printed circuit board which controls the complete boiler.
These Ferroli fans come in two categories:
1) The first category being a 240V driven fan, these fans were fitted to the older non condensing boilers and only have 1 speed, so they are either on or off. They connect to an air pressure switch via heat resistant tubing which couples to the fan via venturies that are located on the fan. This allows the printed circuit board to detect when the fan is running or if it is stationary.
2) The second category being a DC driven fan, these fans are fitted to the newer energy efficient boilers and they can have their speeds varied via the pcb.