The most likely cause of a runny cobbler is using peaches that have not been cooked already. Fresh or frozen peaches will release water into the cobbler during baking, causing a runny texture. This is easily remedied by using canned peaches or by cooking the peaches on the stovetop before incorporating them into the cobbler. Another cause of runny cobbler may simply be that the cobbler was not allowed some time to cool before serving. As the dish cools after baking, the juices will thicken.