Join Date: May 2005
Location: Mayenne France
My Motorhome: Carthago
Thanked 229 Times in 206 Posts
Although the OP hasn't told us which Truma unit he has be it the older C6002 or later Combi types, I'm sure all owners will be familiar with the operation of theses units.
The fan speed is regulated by the exit air temperature and is normal for it to run slowly when first activated then as the temperature of the unit rises it speeds the fan up (often to jet engine speeds) before finding its optimum speed range.
I would deduce from that that there indeed is some form of "intelligent" control for the circulating fan.
I'd be inclined to open all outlets, select the hottest setting on the room stat, turn the unit on and when running, check the discharge of air from each vent, if reasonably similar from each one I'd doubt the problem is one of circulating air.
The most common problem with the C6002 units when suffering from similar symptoms is the combustion air fan, the second most common problem is if the balanced flue pipework becomes disconnected or holed, although that usually is accompanied by unusual noise.