Vaillant questions

[Robbox]

I noticed recently the pressure in the system was below .75bar, so I did the re-pressurisation up to 1.25bar.
So a couple of things I am seeing, when the CH is being fed, the pressure goes to 2bar, then settles back to normal when the CH is not being fed.
The pressure drops over a week or so below .75bar and I have topped it up twice now.
I've checked every pipe, valve etc in the system and cannot find a leak anywhere.
From reading similar posts, it seems the EV might need re-pressurising. I checked the valve and only air came out.
Q1. what is the correct pressure of the EV, would a simple tyre valve device work well to measure it?
Q2. can I use a tyre inflater to pump air in?
Any other areas to check b4 doing the EV?
Thanks!

 

[lightning]

Look in the FAQ it will tell you about pumping up your exspansion vessel

 

[algeep]

check your pressure releif pipe outside isnt leaking if it is then the valve will need replacing and expansion probably depleated which is causing it .when heating up to max temp whats the pressure showing .the system should have been designed and installed so at max pressure doesnt really get above 2-2.5 bar as relief valves opens about3 bar .