What is the pressure in this cylinder expansion vessel?

[RenzoPan]

I was told by the plumber to keep an eye on the pressure, to ensure it stays above 1.0.
The red one is… but the black one is not…. What do the two mean?

 

[snowhead]

The black needle is the pressure reading, showing around 0.6 bar, that's under the 1.0 stated.
The red is just a guide indicator that can be moved anywhere on the dial to indicate a maximum advised upper or running pressure.

 

[RenzoPan]

The black needle is the pressure reading, showing around 0.6 bar, that's under the 1.0 stated.
The red is just a guide indicator that can be moved anywhere on the dial to indicate a maximum advised upper or running pressure.

Thanks.
I’ve checked again and pressure is now above 1.. earlier, I believe the boiler was off, whereas now it’s on. Is it possible for the pressure to change like that?

 

[Chuck]

The normal setting is for the pressure to be 1.0 bar when the system is 'cold' and, based on the position of the red needle, this will rise to about 1.5 bar when the system is operating normally and the thermal expansion of the water increases the pressure.

If this is the first time the pressure has dropped, make a note of the date and reading then top up the system with enough water to bring it back to 1.0 bar when cold. If it's happening regularly consult your plumber as you may have a small leak somewhere.