plumbing is a piece of piss m8 , as above as to whats happened , its a bit like electrics , you cant always see where the pipes(wires) go but they must be there and you knw what they carry !! just need to get yourself familiar on how the combi unit works the rest is easy !!
i fitted my own boiler - even moved it into the loft from the ground floor , took me about 10 hrs and im not even a plumber ! sometimes think i should give up the motor trade and take up plumbing - defo more cash in the job !