Heating leaking

[John D v2.0]

It was you that mentioned it so hopefully you could shed some light on the matter?

I did, my suggestion (to the op) was that it's so at cold there will be a proportion of water in the EV. This means if the system loses a small amount of water it will be replaced from the EV rather than air entering the system at the top.
Since that explanation seems in doubt I'm waiting for someone to propose an alternative.

 

[Wildcat1961]

Considering its not your profession I could quite easily spin you a yarn.
As in 'go pick up a tin of tartan paint'.

 

[John D v2.0]

Considering its not your profession I could quite easily spin you a yarn.

Well you have been spinning me a yarn all day and I'm still waiting for the actual answer! I'm guessing it's a trade secret