Water Pressure Optimal Range for Vaillant Atmotec: Manual vs Electronic Indicators & 1.8bar Issue

Hello!
Is there a service technician or a person familiar with the subject?
How does the manual indicator and the electronic pressure indicator relate to each other, what is the optimal range?
In my case, above the half of the green scale, the electronic shows something around 1.8bar.
At the minimum, as in the pictures, what to suggest?

stefbut wrote:

At the minimum, as in the pictures, what to suggest?

The entire range of the green field is correct pressure. I usually stick to half the scale.

Normal. The electronic Vaillant is reliable and solid. There are practically no faults, sometimes clogging with sediment, but not in this model of the boiler. The pressure gauges have different displacements on both sides and should be regarded as approximate indicators.

Write down whether it is on a cold or a working stove, it will always be lower on a cold one.

On cold, on warm it is before half the scale and about 1.8bar, so what is the correct pressure range from -to?

The pressure with cold water depends on the pressure in the expansion vessel and should be 0.3 bar higher than the pressure in the vessel.
The manufacturer specifies 0.75 bar for the vessel, which gives a total of 1.05 bar as the boiler pressure.
For a larger reserve, a little more pressure can be applied to the expansion vessel, but usually not more than 1.0 bar.
For a pressure of 1.0 in the vessel, this comes out to 1.3 bar in the boiler.

If you have 1.5 bar that's OK. When the water is heated, the pressure may jump another 0.3 bar up, which is normal.
The pressure of up to 2.0 bar with hot water in the installation can be considered within the norm, but it does not make sense to increase it too much.
However, the maximum pressure is 2.5 bar, because a safety valve can shoot between 2.5-3.0, which means a sudden loss of water. If you do not have a sewage hose connected to the safety valve, the water will flow to the floor.

It is worth checking the pressure in the expansion vessel cyclically, but it is checked with the water drained from the boiler and with the drain valve open.