Indeed, going off the information you provided, my first assumption would be lack of water. Without seeing the rest of the system, it's hard to troubleshoot the exact issue. More information is needed.
I will say, most pipes can't handle the capacity of fluids involved with Big/Extreme Reactors setups. You either want the Reactor and Turbine adjacent, with fluid ports touching and correctly configured, or a limitless piping solution. Once you have the system completely filled, you should be able to close the loop, and never worry about it again, but note that some pipes keep a bit of fluid in them, which also need to be filled before the system will close efficiently.