LG Dryer TD-C&0045E does not dry the clothes anymore although everything el?

My dryer does not dry the clothes anymore.The unit otherwise works well. The pump is pumping and the drum is turning, but nothing gets dried.
So I opened the the unit, removed the cover to check if the heater is working. When the heater is attached to the unit it's heating elements barely light up...But when I remove it from the unit so that there is no contact with it, it lights up the sky and gets very hot, but as soon as I make contact with the body of the unit, back to minimal heating.
Anybody with a clue as how this magic works? Do I have to replace the dryer thermostat for it work properly?
Any help would save me buying a new unit. Thank's in advance