Biasi M90 Combi Boiler fan cycling off and on

Hi All,

My newly installed Biasi M90 Combi boiler makes a loud whirring noise for about three seconds before firing up. It is a quite annoying thing. Has someone faced this issue earlier if yes, and then please tell me how I can fix it?

Thanks a lot


Hi Ben,

I think the fan in your boiler is not working properly. Like some other boilers, we can narrow down the fan faults on your Biasi combi boiler into the following:

  1. Damage or loose connections/wirings
  2. A faulty printed circuit board
  3. Defective air pressure switch

You have to call a boiler engineer, as he will determine where a fault lies within the:

  1. Wiring
  2. Air pressure button
  3. Printed circuit board
  4. Fan

Sometimes, this issue can be fixed easily by just repairing the connections/wirings. On the other hand, in some cases, replacement parts are required