Strange whiring noise from boiler

[forrest1066]

Hello Everyone

Dont know if anyone can help me we have a Vokera 80SP when the heating is on and we start up the hot water then knock it off and it goes back to heating the boiler starts to make a whirring noise, yet if you turn down the room thermostat to switch the boiler off and then turn it back on again everythings fine. the entire system is working fine and there are no problems but for this noise?? does anyone have any ideas??

Thank You

 

[Phoenix Heating]

could be the fan starting to wear out (assuming it has one....not familiar with this model) hope this helps