How to repair leaks/remove pump on Ferroli Optimax HE 31C Super plus?

I had a fault code with my Ferroli Optimax HE 31C Super Plus showing it was a return sensor fault. I found that a leak from the return pipe just above the sensor had shorted it out. I bought a replacement sensor and attempted to repair the leak. I am a new gas safe registered heating enginerr so though it wouldnt be a problem.... wasnt i wrong!!! It appears that you need to take the pump out to remove this return pipe but can find how to get the pump out!!! Can anyone please give advice or help???