Yep, if the fermenter was sealed, then mold indicates an infection. Could've happened when you took that last sample. Heat doesn't spontaneously form mold...mold spores are needed.
Re-think your sanitizing habits, and the environment around the fermenters. did some dust from above fall in when you took that last sample? etc
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10