Yorkieben is right indeed - took his acid test advice, it's been running upside down all afternoon, and is as cool as a cucumber. Looks like I'll have to tell the guys at Scan.
Thanks all - I'll probably RMA this.
n.b. - I've been running it with all fans on full, and the case side off, since I got it working again, and it's been fine, but obviously this isn't a permenant solution! That said, when it's cool enough, this board is the nuts.
Cheers again,
MB