Who fitted the 13A fuse?
FCUs come with a 13amp fuse fitted. That is the largest permitted. In my opinion, they should be sold with the SMALLEST fuse size.
The unwary/don't care brigade dont even give it a thought nor read the installation instructions of the device to determine the required value of the fuse.
All too common, I'm afraid. And we will see more of it now that electrical work in kitchens is no longer notifiable