How are you heating the enclosure? Do you have a light and/or an undertank heater? Under tank heaters should only cover about 1/3 of the surface of the tank. If you are using both, then lower the watt of the bulb, and if that doesn't work, depending on what reptile you're housing, you may be able to get rid of the light altogether.
Nocturnal species do not need a light source, but diurnal species do.
Make sure that if you are using both an under tank heater and a light, that you have them both on the same side of the enclosure.
Is there any difference in the temperature between the hot and cool side? As long as there is a place where the reptile can go to cool off, then getting a low-low temperature is not necessary.