My pump to my shower keeps cutting out after 15 mins and no water?

I have a 3 bar salamander negative head pump that has only just recently been replaced. It is connected to my cold water storage tank about 60l, in my flat and also to my mixer taps and shower. It now runs for 15 mins and then the pump cuts out and theres no water flow at all? Any ideas what is wrong as I would think that the hot water would just run cold but no run out of water!?