My Chaffoteaux britony combi se has 40 80 fault?

My boiler goes out and won't come back on , I took the front off to have a look thinking that it could be the pump , the red light is showing ( reset ) the pump seems OK , When I moved the two black cables which go to a pressure switch at the back of the pump by accident and we had action like it was a loose connection , got it going again but every morning when the heating should go on, it doesn't and the red light is on. I move the two black cables again and away she goes. Today I rang tec and they said that I need a new pressure switch Part number 61310364.
its right at the back of the pump and attached to it . can anybody tell me , is it easy to fit please ? any Tips
Thanks John