Fresh water tank don't take water?

First time trying to use our 100 gallon tank on carbon 33. Open door, removed cap, tried to put water in slowly and it just spits it back out...won't take any. I have the potable water drain valve open all the way to see if water was in it but nothing....any ideas or thoughts as to what might be preventing? If just air I would think it would take some slowly...is there a valve with the water pump or something that might be closed? Thanks