So with the 2 litre expansion vessel having a charge of 1.9bar it won't really effect its performance in this case? The ones usually get are silver with a pre-charge of 3.5 bar I believe. The standing pressure of the system is 4 bar. No pressure reducer is currently fitted. I'm adding controls to a little under sink heater that at the moment has a vented tap that is broke. And a replacement is around £100. So cheaper to add a 6 bar pressure relief below the sink and expansion. Cold water draw off too close to allow expansion in to the mains