Some boilers have what is known as a pump overrun, so the pump is connected to special terminals specifically for it at the boiler. That way the pump can continue to run after the boiler has switched off to get rid of residual heat.
This is the type of system shown in the diagram that you posted earlier. In this case, PL is the terminal for 'Pump Live' and ptobably because you posted this diagram no doubt will be why
@dilalio gave you the answer that he did.
However, other boilers don't have this facility, and looking at the wiring diagram for the WB 70/90 below, I don't see any pump wiring terminals, so it appears that yours doesn't.
Where there isn't a pump overrun, the pump will be controlled by the orange wires from the motorised valves exactly the same as the boiler is, so that the pump and boiler will be switched on and off together. In which case, the diagram below would apply. You can see that the Pump and Boiler N E L are connected together at the wiring centre as
@The Novice has said.
I have seen a few instances where the pump N E L has been connected directly to the boiler N E L instead of being connected via a wiring centre, or even directly to the orange wire at the motorised valve. It depends upon the personal preferences of the original installer, and the layout of the various heating system components in your home. As you system was only for heating, originally you may not even have a full wiring centre, just junction box or two.
