Installation instructions for Ferroli 30800009?

I have bought a Ferroli Radio Thermostat Clock (Part No. 30800009) to fit to my Ferroli Optimax HE Plus 31C. I was told by somebody that it was very easy. I've found the installation and User Instructions online and the picture is the same as the one I have but in the instructions it only shows the sender unit that wires into the boiler as having four connectors whereas the one I have has five so I'm not sure which to connect. Does anyone have any advice on this