[Solved] De Dietrich MCR3 EVO 24T stove - error code A, installer icon and CODE inscription are displayed

Respect.
Last evening I went into the basement to raise the temperature of the central heating a bit, I stood in front of the stove, and on the display, alternating with the pressure (1.3 bar), a large letter A and the installer's symbol appear in the very center.
I will add that I didn't have time to click anything before it was displayed.
When I tried to use any button (I started with +, because that's how you raise the temperature on the central heating), none of the buttons respond. After holding the R button, the word CODE appeared on the display and the stove stopped working. I studied the installation, operation and maintenance instructions, I tried to hold + to display (to "enter") the access code to the installer menu (because that's the only option I found in the instructions for this CODE), but nothing happens.
I reset the furnace mechanically (by cutting off the power source). After switching on, after a while, the display shows the central heating pressure and the letter A with the installer icon, or the temperature (when it starts heating) alternating with the letter A and the installer.
I'm so lucky that the stove started heating again with the parameters set a month ago, but I can't raise its temperature in any way, neither for domestic water nor for central heating.
Trying to enter the menu doesn't work either.
I called the service technicians, but it looks like they have the weekend because no one answers...
Do you have any ideas how to solve this?
Thank you in advance for your help.

Specify exactly what is displayed and what happens next

A and water pressure in the central heating/or temperature appear alternately when the stove heats up the water. Additionally, there is an installer icon (a guy with a key) that flashes all the time.
This A is in the very center and nothing except the installer icon appears there anymore.
On average, A is displayed for 4-5 seconds, and e.g. the temperature during heating for about 10 seconds and that's all.

Added after 15 [minutes]:

I am sending a photo and a short video as attachments.
I'm sorry that I wrote it in a separate post, but when I wanted to edit it, it didn't load the attachments, an error popped up.



Edit: I managed to enter the menu and restore factory settings, but still the same...

How many runs do you have? Do you have a cMix kit? Some regulator, e.g. iSense?

1 hot water circuit and one central heating circuit supplying all rooms in the house. No regulators, external drivers, etc.

Hello, did your situation become clear because I have the same problem?

Isn't this a reminder to inspect your furnace annually?

I have the same...

Added after 22 [minutes]:

Approx. Controlled this is a notification about the burner operation service. If you service the furnace normally and want to remove it, you must reset the furnace to enter the installer menu according to the manual, enter the AP010 parameter and set it to 0 and confirm. That's all. What you did with the factory settings was not a good idea because you now set a lot of options that are not necessarily correct.
Regards

And how does this furnace reset?...

Turn off the power for a moment and turn it on

exactly as gbureczek1982 wrote. I'm sorry I didn't close the topic earlier. Problem solved.