HOW CAN I FIX MY INDESIT ISL65C TUMBLE DRYER?

I took the back off my tumble dryer and pushed a pin into the thermostat which released it back to normal, this advice was given by the company who sold it to me, it worked for a short time and now I have just done it again, the dryer heats up fine for about 10 mins then goes cold again, i can reset the thermostat again but this is becoming very annoying. Do I just need to buy a new thermostat or could there be something else causing the problem.

Your help and time in this matter is much appreciated