S Plan? Do you mean this?Is there a zone valve for the heating?
Can you post a picture of the flue and external pipes?
The old cylinder overflow pipe was hooked into the wall & over a window, now hooked into the plastic going down left & connected to what was there. Said OK as used push connections?
Pipe to right now bossed into stack is from below the boiler? There was another original pipe sticking out, now removed, not sure what that was, overflow?