I noticed condensation inside the glass tube of my heater, does that mean it is defective or broken?
No, simply seeing condensation inside your Aqueon Glass Adjustable Heater does not that it is broken or defective. Check that the heater is working properly by using a thermometer with your fish tank. (also make sure that the water is the right temperature for the type of fish that you have inside your fish tank). The reason you may see condensation is because humidity was in the air and trapped inside the tube when it was manufactured and sealed. Your heater is still able to perform properly with this condensation.