I'm sorry Julian, I'm not clear in my mind how your system is going to be laid out, it will probably work ok
Desp
To ease my effing conscience

The relative position of the F/E and Vent is important to stop pumpover etc,
The relative position of the vent/boiler is important to provide safety.
From what you say it sounds as if, if your boiler has a hissy fit it can only vent itself through the T/S, which is not good.
Edited cos I'm a stobborn git
