Many T owners have reported a situation where the Truma fan kicks in to high gear and blows a ton of hot air throughout the van. It’s pretty annoying. The common element when this has occurred is that they had the Truma set for both heat and hot water and the Truma decided that it (the Truma) was overheating so it kicked into an exhaust mode to cure the problem – and sometimes throws an overheating error code, which clears once the unit has cooled down.
Simple enough to avoid having this happen – don’t run heat and hot water at the same time.