wiring a honeywell cm900 to worcester 28cdi

[nickcrow]

Is this something i could do my self
I have got 2 wires (1 blue 1 brown and earth not connected) coming from the boiler to the existing unit which i want to replace with the honeywell cm900 dont understand the wiring instructions could someone tell me which wires to attach to which terminals they are labelled a b and c on the honeywell is it straigt forward complete novice help much appreciated

 

[twgas]

I wouldn't advise a complete novice to do anything, however, your's and my descriptions of a complete novice may differ.
What is the make and model of the old unit?

 

[nickcrow]

its a PT5