Biwar Viking 55L Boiler: Water Pressure Rises to 8 Bar at 50°C with Pressure Reducer & Manometer

Maybe this will help in the discussion

https://www.elektroda.pl/rtvforum/topic2391906.html

http://www.zawor-do-bojlera.pl/

retrofood wrote:

..... An anti-contamination valve should be installed in the installation, which prevents the backflow of water, as it could contaminate the entire water supply system ...

However, such a valve is connected to the building at the "input" (I have the same one), unless it is required for each apartment separately in multi-family buildings. But certainly not with the boiler in the apartment. As for the complete elimination of dripping (or significant reduction), it is only an expansion vessel.

BrucieK wrote:

But if this safety check valve allows hot water to return to the cold system, there is probably a risk that the entire system will be contaminated with Legionella, right? ....

The anti-contamination valve can be operated at the operating limit, i.e. right behind the water meter. Nobody assumes that everyone is spreading legionella in boilers. Nomen omen, legionella can also settle on the water supply side - in sections of the network where, for various reasons, water consumption is very low or there is no water at all. Before he develops this legionella in his colleague Jaskiniowiec24 in the pipes, it is highly probable that he will have time to bathe several times and simply rinse the pipes on the light, thus preventing the development of the creature. By the way, if you know the structure of the diaphragmatic vessel, be aware that the conditions for the development of legionella in this vessel are IDEAL.

BrucieK wrote:

... If a safety valve and a diaphragm vessel are installed, I do not see any sense for the hot water to flow back into the cold water system in order to reduce the pressure.

And you are absolutely right - except that we are also considering a case where the user simply has no place to install this vessel in the world.