Fan motor failed or PCB.
Which you'll have seen when you did a Google search for yourself, I'm sure.
Check the second to last entry here:
http://www.upperplumbers.co.uk/plumbing/plumbing_pages.php?title=Worcester&cat=12
Mentioned in the manual here - download and keep
https://www.worcester-bosch.co.uk/support/document/download/release/6720812177/12515
XXX, January 2016