Ariston Fan Assembly 999204 is the device that introduces fresh air in to the combustion chamber, allowing the gas to be burnt correctly it also extracts the noxious gas after the combustion process is complete. The boiler has safety parameters in place to make sure no gas can be passed through to the main burner if the fan is not functioning correctly. Heatingspares247.com is one of the UK's largest independent Boiler Parts & Heating Spares Stockist, We specialise in the supply of Genuine Spare Parts along with all the leading manufacturers. Services available are trade counter pick up, Next working day standard delivery, next working day AM delivery and Saturday delivery. We also operate same day express delivery service. Our Opening timers are Monday to Saturday, 8AM to 5.30PM Heatingspares247.com is an Approved Boiler Spare Parts Stockist, and we guarantee to supply Genuine Heating Spares from the Boiler Manufacturers.