Error E9 on Junkers Stove After 3 Months: Resolving Zero Pressure & Water Filling Issues

Hello
After buying the house, I had a Junkers service technician to start the stove. After his visit, the stove was turned off. Today 3 months pass when I would like to start using it and surprise because after switching on the power the error e9 appears. I take my instructions and read. I rule out all causes. Looking at the pressure gauge and there is still 0. Deflection of the pressure valve and still 0. After about 15 minutes turn on the power again and 2-3 can be heard as if the stove took in water but still on the pressure gauge 0 and error e9. I check all valves open - closed. Checking if there is water in the taps despite the main water valve turned on (to be sure). I repeated the action twice and still e9. I called the service technician who started the furnace and heard that I had to wait 5 to 30 minutes for water to fill the installation, check if the water valve was turned on. The service technician does not understand that the water is on, the radiators are on. All the time claims that there is no water. Only that it concerned myself.

Has anyone had such problems with the new furnace? Cerapur Midi ZWB 24

You must allow water for the central heating system to a value of about 1 Bar. You can find it in the boiler manual on page 12.

Usually, the diaphragm vessel is factory set at 0.75 bar, therefore I would treat the initial pressure of 1 bar on the boiler as an acceptable minimum, and not normal daily pressure.
As a result of venting, etc., small pressure losses may occur, which is why in my opinion it is safer to keep 1.2-1.5 bar on a cold day. As the boiler is operational, after heating the water, the pressure will increase by approx. 0.2-0.3 bar, so it will still be a safe value below 2 bar, i.e. with a large margin to release the safety valve.
Some boilers have precise pressure gauges with a 0.2-bar graduation, so you can easily dose pressure with an accuracy of 0.1 bar, while others have a 0.5-bar graduation, so the pressure setting on the boiler automatically decreases and it is harder to notice small pressure losses.